GCSE Science podcasts - Energy

JAMES: Hello and welcome to the BBC Bitesize Physics podcast.

ELLIE: The series designed to help you tackle your GCSE in Physics and combined science.

JAMES: I'm James Stewart, I'm a climate science expert and TV presenter.

ELLIE: And I'm Ellie Hurer, a bioscience PhD researcher.

JAMES: And in this podcast, we're going to be your physics guides. Yes, we are. From forces to electricity, energy to gravity, we are going to explore some of the most important facts you need to know to revise for your exams.

ELLIE: And if you want to really get into it, be sure to grab a pen and paper so you can make notes and try out equations throughout the episode.

JAMES: This is episode one of our eight-part series all about energy, and today we'll be talking about energy stores and systems.

ELLIE: So let's begin.

JAMES: Energy is converted in a variety of ways, but the three most common ways are through heating, work done by forces, and work done when a current flows.

ELLIE: There is one key fact that you definitely need to know about energy.

Energy can't be created or destroyed. It can only be transferred usefully, stored, or dissipated.

JAMES: Dissipated means it's wasted, usually by being lost to the surroundings. So let's explore what that actually means when it comes to how we interact with energy on a daily basis.

ELLIE: So let's say you want to make a cup of tea. You go to the tap to fill the kettle up with water, plug the kettle into the wall, then switch it on until the water begins to boil.

JAMES: How is energy being transferred as you boil that kettle? What effect does the heating have here?

ELLIE: Well, the kettle is powered by electric energy, and that store of electrical energy is transferred into the thermal energy store in the water that's in the kettle.

JAMES: Any other energy transfers happening in there?

ELLIE: Well, it's not just the water in the kettle that's getting hotter. The kettle releases steam and thermal energy that heats up the surrounding area.

JAMES: But because you didn't turn on the kettle for the purpose of heating up the room, that energy is dissipated, it means it's wasted.

ELLIE: Yep, correct. When we describe the way that energy is converted, we sometimes describe the objects that are part of this process as a system. And different systems store and transfer energy differently.

JAMES: Energy is also transferred through work done. We cover work done in much more detail in our Bitesize Physics ‘forces’ series, so be sure to go back and check that one out. But for a quick definition, work done is when a force causes an object to move through a distance, when a force transfers energy from one store to another. So let's look at an example of how work done by forces changes the energy in a system.

Imagine you're at the park and decide to go and sit down on the swings. What a nice day. You push yourself up and down until you're having fun on the swings. But as you are, you're causing an energy transfer.

ELLIE: When you push, you transfer energy from the chemical energy store in your leg muscles to the kinetic store in the swing.

JAMES: Yes, and when you're up really high in the air, that kinetic energy becomes part of the gravitational potential energy store in the swing. Before being transferred back into the kinetic energy store as you come back down again.

ELLIE: So let's talk about one final energy transfer. And for this one, we're heading to the seaside.

JAMES: Ellie, imagine you're on a boat.

ELLIE: Just a boat?

JAMES: Fine, a yacht. A super yacht. Whatever you want.

ELLIE: That's better.

JAMES: Alright, imagine you're on a full blown, glamorous, mega yacht with ten bedrooms on board, swimming pool, private chef, and what about a DJ playing along with your favourite songs? Sound better?

ELLIE: Sounds like my dream.

JAMES: Good.

ELLIE: Right, we're going to give you examples and get you to answer what energy transfer you think is going on. So grab your pen and paper.

JAMES: Okay, so if the motor that drives that yacht is powered by diesel, what energy transfer is going on? I'll give you a few seconds to think about it.

ELLIE: If the motor that drives the yacht is powered by diesel, the yacht transfers energy from the chemical energy store of the fuel into the kinetic energy store of the boat as it gains speed and travels.

JAMES: But are there other energy transfers happening in there as well?

ELLIE: Yeah, some energy would also be transferred into thermal energy, heat, which is wasted energy in this case.

JAMES: Okay, let's recap the three facts we covered today. Number one, energy can't be created or destroyed. It can only be transferred usefully, converted or dissipated.

Number two, a system is an object or group of objects and there are changes in the way energy is stored when a system changes.

And thirdly, energy is converted in a variety of ways. But the three most common ways are through heating, work done by forces, and work done when a current flows.

ELLIE: Thank you so much for listening to Bitesize Physics.

If you found this helpful, go back and listen again and make some notes so you can come back to them when you revise.

JAMES: Yeah, super helpful. In the next episode of Bitesize Physics, we are going to be talking all about kinetic energy and gravitational potential energy.

ELLIE: Until next time…

BOTH: Bye!

ELLIE: Hello, and welcome to the BBC Bitesize Physics podcast.

JAMES: The series designed to help you tackle your GCSE in Physics and combined science. I'm James Stewart, I'm a climate science expert and TV presenter.

ELLIE: And I’m Ellie Hurer, a bioscience PhD researcher. Just a reminder that we're covering lots of different aspects of energy in this series, so make sure you take a look at the rest of the episodes too.

JAMES: Okay, let's get started. Today, we're talking about the types of energy that stretch things, get us moving, and bring us back down to earth. Elastic, kinetic, and gravitational potential energy. Woo!

When an object is in motion, it has energy in its kinetic energy store. So a football flying in the air, a car driving down the street, a leaf falling down from a tree. They are all in motion, so they possess kinetic energy.

ELLIE: And you can calculate the kinetic energy of a moving object using an equation. So grab your pen and paper to write this one down.

Kinetic energy equals 0.5 multiplied by mass multiplied by speed squared. Let me repeat that in case you didn't get the chance to write it down. Kinetic energy, which is measured in Joules equals 0.5 multiplied by mass, which is measured in kilograms, multiplied by speed squared, and speed is measured in metres per second.

JAMES: Yeah, so let's say it's a really nice day and I decide to ride my bike through the park, and I want to measure my kinetic energy store, a reasonable thing to do. I would take 0.5 and multiply it by me and my bike's combined mass of 100 kilograms. Then, I would multiply that by my speed, which is 5 metres per second. So, 5 squared is 25. So, 0.5 times 100 times 25, to get the answer 1,250 joules.

ELLIE: So, the next thing we want to talk about is gravitational potential energy. In our Bitesize Physics ‘forces’ series, we give gravity its own episodes, so be sure to go and listen to that after this.

JAMES: Yeah, but just as a quick explanation, gravitational potential energy is the energy an object has because of its position above the surface of the earth.

ELLIE: In other words, gravitational potential energy happens when an object is lifted from the ground. The higher it is, the more gravitational potential energy. Also, the greater the mass of the object, the more gravitational potential energy.

JAMES: Many things around us have gravitational potential energy. Things like a balloon flying in the air will eventually fall.

When we jump, we end up back on the ground. And when we throw confetti up into the sky, it floats back down.

ELLIE: And to calculate the amount of gravitational potential energy an object gains by being raised above the ground level, we use a specific calculation. So I think it's time to grab your pen and paper again.

JAMES: Gravitational potential energy equals mass multiplied by gravitational field strength, multiplied by change in height. The gravitational field strength of any object on earth is 9.8 newtons per kilogram

ELLIE: Gravitational potential energy is measured in joules. Mass is measured in kilograms. Change in height is measured in metres. And gravitational field strength is measured in newtons per kilogram.

JAMES: Should we apply that to a real-life example?

ELLIE: I think so.

JAMES: Yeah, okay.

ELLIE: So, on a scale of 1 to 10, how good are you at juggling?

JAMES: I'd go with a solid 2.1.

ELLIE: In that case, I won't give you the fire baton.

JAMES: Okay, let's just practise with one baton. No flames?

ELLIE: Sounds good.

JAMES: OK, so to calculate the gravitational potential energy of the baton as it flies in the air, because that's what I do on the weekends. We would need to know its mass and change in height.

ELLIE: And we’re going to make this a calculation for you to figure out, so grab your pen and paper.

JAMES: Right, let's say the baton has a mass of 2 kg and you throw it up 3 m in the air. If the equation is gravitational potential energy equals mass, multiplied by gravitational field strength, multiplied by change in height, what would be the gravitational potential energy of the baton?

ELLIE: If you missed the measurement or the equation, be sure to rewind 30 seconds. But we'll give you a few moments to pause, write that down, and calculate it.

JAMES: Okay, so hopefully you've had a few moments to work that one out, but let me explain how we would calculate that. So to find out the baton's gravitational potential energy, you would multiply the mass, that's 2 kilograms, by the earth's gravitational field strength, that's 9.8 newtons per kilogram, by the change in height, that was 3 metres. To get the answer, drumroll please 58.8 joules.

ELLIE: That is the gravitational potential energy of the baton when it's at its maximum height. But while it's still going up there is a transfer from the kinetic energy store to the gravitational potential energy store. The kinetic energy store decreases as the gravitational potential energy store increases.

JAMES: And when the baton is on the way down, the opposite happens as the gravitational potential energy store decreases and the kinetic energy store increases. The transfer is really important to remember as it often comes up in exam questions. So again, if you haven't already, be sure to write that down.

ELLIE: And now for the final part of this episode, let's talk about elastic potential energy.

JAMES: Elastic potential energy is the energy objects’ store if they are stretched or squashed. You can calculate it using an equation, of course you can. So get your pen and paper out one last time, hopefully you haven't taken them.

ELLIE: Are you sure it's one last time?

JAMES: I don't know, I can't, don't hold me to that.

Elastic potential energy equals 0.5 multiplied by the spring constant multiplied by extension squared. So the spring constant measured how stiff the spring is. The larger the spring constant, the stiffer the spring and the more difficult it is to stretch. An extension is the way the length of an elastic object changes when you stretch or you compress it.

So let me repeat that formula again. Elastic potential energy, measured in joules, equals 0.5 multiplied by the spring constant, measured in newtons per meter, multiplied by extension squared. An extension is measured in metres.

ELLIE: Let's apply it to a spring, and we were lying, because you need to grab your pen and paper, again, so you can write these calculations out.

So let's say this spring in your hand has a spring constant of 3 newtons per meter, and it's extended by, let's say, 50 centimetres. How would you calculate its elastic potential energy, if the equation is elastic potential energy equals 0.5 multiplied by the spring constant, multiplied by extension squared.

JAMES: If you missed a measurement, there are quite a few in there or the equation. Be sure to just rewind 30 seconds. Super easy, but we'll give you a few moments to pause. Write that one down and calculate it.

ELLIE: Okay. Did you get a chance to try and work it out? I'll walk you through it step by step, so don't worry.

First, let's convert the extension into metres. So 50 centimetres is equal to 0.5 metres. The equation uses extension squared, so we would do 0.5 multiplied by 0.5, which is equal to 0.25. To calculate its elastic potential energy, you would take 0.5 and multiply it by 3, and then multiply it by 0.25. And this would give you the answer of 0.375 joules.

JAMES: But, a really important thing to remember is that the equation only applies when the limit of proportionality has not been exceeded. And the limit of proportionality shows the maximum amount of force that can be applied to an object before it changes shape permanently.

ELLIE: And if you want to learn more about elasticity, be sure to head over to the ‘forces’ series of Bitesize Physics to hear more.

So James, I think it's time we do a recap because there was a lot going on in this episode.

JAMES: There was.

ELLIE: So the three key facts that we covered today are: the formula to calculate kinetic energy, which is kinetic energy is equal to 0.5 multiplied by mass, multiplied by speed squared.

The formula to calculate gravitational potential energy is mass, multiplied by gravitational field strength, multiplied by height.

And finally, the formula to calculate elastic potential energy is 0.5 multiplied by spring constant, multiplied by extension squared.

JAMES: And hey, this is just the start. We're going to be diving into a range of other types of energy transfer as the series goes on, starting with thermal in the next episode about specific heat capacity. So be sure to keep listening.

ELLIE: So guys, thank you for listening to Bitesize Physics. If you found this helpful, go back and listen again and make some notes so you can come back to this as you revise.

BOTH: Bye!

JAMES: Hello and welcome to the BBC Bitesize Physics podcast.

ELLIE: The series designed to help you tackle your GCSE in Physics and combined science.

JAMES: I'm James Stewart, I’m a climate science expert and TV presenter.

ELLIE: And I'm Ellie Hurer a bioscience PhD researcher.

JAMES: And just a quick reminder that whilst you're in the BBC Sounds app, there's also the Bitesize Study Support podcast, which is full of tips to help you stay focused during revision and get the best out of your exam day.

ELLIE: Yeah, it's definitely worth checking out. So okay, let's get started. Today we're going to be talking about specific heat capacity.

James, do you like cooking?

JAMES: I do, I do indeed.

ELLIE: What's your favourite thing to make?

JAMES: Oh, I love a good roast, but I'm also like so impatient and it gets, takes so much time, but when you get it, it's so satisfying. How about you, Ellie?

ELLIE: I’ll be honest. I just really love pasta.

JAMES: That's fine! I like it, good!

ELLIE: It’s quick, easy and delicious. And it's the example we're going to use a lot today as we talk about heat.

So, when you heat food, or any material, the particles heat up and transfer energy from their thermal energy store to their kinetic energy store and they start moving faster. Which is why you sometimes see your food sizzling away when you've warmed it up.

JAMES: Yeah, looks good, doesn't it? And as you'll note, if you've ever looked at all the settings on a microwave, different materials require different amounts of energy to change temperature.

The amount of energy they need depends on the mass of the material, how much you want the temperature to change, and the substance.

ELLIE: And that last one is what we're going to focus on, the substance of the material, because that's what determines a material's specific heat capacity.

JAMES: Specific heat capacity is the amount of energy required to raise the temperature of one kilogram of a substance by one degree Celsius. So in your case, Ellie, that will be the amount of energy you need to raise a temperature of one kilogram of water by one degree Celsius.

ELLIE: So, let's talk about how to calculate the change in thermal energy that occurs when we heat something up. Grab a pen and piece of paper because it's time for a formula.

JAMES: We need, like, a klaxon, don't we? Or a bleep or a buzzer of some kind there.

Okay, so change in thermal energy equals mass multiplied by specific heat capacity, multiplied by temperature change.

I'll say that again with the units that we measure those in. So change in thermal energy is measured in joules, and to calculate it we take the mass of a material, measured in kilograms, multiply it by the specific heat capacity, measured in joules per kilogram degrees Celsius, and then we multiply it by the temperature change measured in degrees Celsius.

ELLIE: So just take a note that you might have to change the mass of a material into kilograms. So you need to remember that 1,000 grams is equal to 1 kilogram.

JAMES: That's handy to know. My partner's a baker and like, that's every day in my house, the conversation, “How many kilograms is that?” like, every day.

ELLIE: So yeah, you can use this in everyday life.

JAMES: Yeah, literally. It applies to all circumstances.

ELLIE: So, let's talk about how to apply that to a practical example. Imagine it's a Friday night, you're chilling, and you want to boil some water to make some pasta.

JAMES: So you might take 0.5 kilograms of water and heat it up from 20 degrees Celsius to 100 degrees Celsius. And water has a specific heat capacity of 4,180 joules per kilogram per degree Celsius. So how would you work that out? I'll give you a few seconds to take the equation, write it down and calculate it for yourself.

ELLIE: Okay, did you finish your calculations? Let me explain. So, you would multiply 0.5 kilograms by 4,180 joules per kilogram per degree Celsius. Then, you'd multiply that by the 80 degrees Celsius temperature change to get the answer…

JAMES: 167,200 joules.

ELLIE: That's correct.

JAMES: Wahoo!

ELLIE: Woo!

JAMES: So imagine you wanted to make some iced coffee. I love iced coffee.

ELLIE: That's my favourite.

JAMES: Yes, always my order. Even if you made your hot coffee and gave it a few minutes to cool down, it still wouldn't be cool enough as a refreshing cool drink on a summer's day. So, you'd pop it in the fridge, wouldn't you?

ELLIE: Yeah, but how would you calculate the thermal energy change between you putting it in the fridge and then taking it out to drink the next day? Well, it's time to grab your pen and paper again because it's time for another calculation.

JAMES: The equation to calculate change in thermal energy is mass multiplied by specific heat capacity, multiplied by temperature change.

ELLIE: So, if the mass of the coffee was, say, 0.2 kilograms, the specific heat capacity of the coffee was 4,180 joules per kilogram. And if it was cooled down from 80 degrees Celsius to 3 degrees Celsius, how would you calculate the thermal energy change?

JAMES: If you missed a measurement in that or you missed the equation, be sure just to rewind 30 seconds and listen back, no problem. We'll give you a few moments to pause, write that down and calculate it.

Okay, so to calculate the heat change, you would simply multiply 0.2 kilograms by 4,180 joules per kilogram per degree Celsius. Then you multiply that by minus 77 degrees Celsius temperature change to get the answer…

ELLIE: Minus 64,372 joules

JAMES: Yes, that's right. And look, we know there's a lot of numbers and measurements in what you've just heard, so be sure to check out the BBC Bitesize energy and heating pages to read the formula and apply it to your own range of examples.

ELLIE: So, it's that time that we need to go through key points that we've learned today. So firstly, different materials require different amounts of energy to change temperature. Also, the specific heat capacity of a substance is the amount of energy required to raise the temperature of one kilogram of the substance by one degree Celsius.

And finally, the equation to calculate change in thermal energy is: change in thermal energy is equal to mass multiplied by the specific heat capacity, multiplied by temperature change.

JAMES: Alright, so those are some of the key facts you need to know about specific heat capacity and in the next episode, we're going to be talking about how to apply what you've learnt to the practical every day. So, get ready to get stuck into that.

ELLIE: Thank you guys for listening again to BBC Bitesize Physics. If you found this helpful, go back and listen again and make some notes so you can come back to this as you revise.

BOTH: Bye!

ELLIE: Hello and welcome to the BBC Bitesize Physics podcast.

JAMES: The series designed to help you tackle your GCSE in Physics and combined science. I'm James Stewart, I'm a climate science expert and TV presenter.

ELLIE: And I'm Ellie Hurer, a bioscience PhD researcher. Before you listen, just a reminder that you can listen to the whole series or find an episode that you want to focus on. Whatever works for you.

JAMES: Okay, let's get started. Today we're going to be talking about the specific heat capacity practical. So Ellie, you might be wondering why we're wearing lab coats today.

ELLIE: Yeah, I was a little bit confused when I saw your text saying we needed lab coats, safety goggles and a clipboard to record a podcast. It's not exactly a dangerous activity.

JAMES: It’s a serious job, Ellie. You never know when a microphone might jump at you, a script might give you a paper cut or a listener might leave a mean comment because, well, they don't like our jokes.

ELLIE: Our jokes are great, so that's not going to happen.

JAMES: Ha, ha, ha. Look, we're off topic. The reason we're in lab coats today is that part of GCSE physics includes a practical activity all about specific heat capacity. Finally, a practical.

If you haven't listened to that episode about specific heat capacity, please do pause, go back and listen and then return to this episode and come back and do it with us. As a quick reminder, specific heat capacity is the amount of energy required to raise the temperature of one kilogram of a substance by one degree Celsius.

ELLIE: And when it comes to your GCSE, you'll carry out a practical investigation to determine the specific heat capacity of one or more materials. Let's try an example.

JAMES: As a heads up, we're gonna go through quite a few definitions and steps you'll need to understand for this practical. So, classic us, if you haven't already, get your pen, get your paper and let's do it together.

So in this practical, the aim of the experiment is to find out the specific heat capacity of a sample of material.

ELLIE: The independent variable is the material the block is made from. In this case, you'll use an aluminium block that will have two holes drilled into the top that don't go the whole way through.

JAMES: The dependent variable is the specific heat capacity value, and the control variables are the time the heater is on for and the mass of the material used.

ELLIE: Okay, so let's walk through how you would do the experiment step-by-step. So step one, unless you know your block is exactly one kilogram, measure the mass of the block using a balance.

JAMES: Step two, place the immersion heater into the central hole at the top of that aluminium block.

Step three, place the thermometer into the smaller hole of the block and put a couple of drops of oil into it just to make sure the thermometer is surrounded by hot material.

ELLIE: And step four, fully insulate the aluminium block by wrapping it loosely with cotton wool.

And step five, record the starting temperature of the block.

JAMES: Yeah, so far so good. Step six, connect the heater to the power supply and of course don't forget to turn the power supply on. Time it for 10 minutes and then turn the power supply off again. There also needs to be an ammeter in the circuit so the current can be measured.

And then finally, step 7, after 10 minutes the temperature will still rise, even though the heat has been turned off, and then it will begin to cool. So, record the highest temperature that it reaches and calculate the temperature rise during the experiment.

ELLIE: And as you do the practical, you'll need to measure four key things. The current reading from the ammeter, the voltage reading from the power supply, the initial temperature in degrees Celsius, and then the final temperature also in degrees Celsius.

JAMES: And when you do this practical in class, you'll then take your measurements and analyse them to calculate the specific heat capacity of the block of metal you used.

ELLIE: And to learn more about the equation you need to use to calculate this, head over to the Bitesize website to read more.

JAMES: Then repeat the whole method with another material, as that is the independent variable being investigated.

ELLIE: Always remember that no experiment is perfect. Sometimes we run into something called an experimental error, which is when our results aren't completely accurate because of other variables.

So, can you think of any we might find in this experiment?

JAMES: Well, one variable could be that not all of the heat from the immersion heater will actually heat the aluminium block. Some will be lost to the surroundings.

ELLIE: Exactly, James. That means that more thermal energy is transferred than is necessary for the aluminium block alone, because some of the energy is transferred to the surroundings.

JAMES: Which means the final result of our specific heat capacity will be higher than what is actually needed for one kilogram of aluminium alone. So, it's really important to know that other variables will affect your practical.

ELLIE: Because this is a practical experiment, there are some things we need to do to make sure the experiment is safe and that the results are accurate.

JAMES: Yeah, in this experiment we're working with an immersion heater, which can get very hot very quickly, which of course is a hazard, it can burn our skin. So, what measures Ellie, should we take to control that hazard?

ELLIE: Well, firstly, you wouldn't touch the heater when it's on. You would also position the apparatus away from the edge of your bench to reduce the risk of it falling. As well as that, once you're done with it, you would give the heater time to cool down before packing it away. Sometimes you'll be given a method that isn't quite right and the exam will ask you to suggest how to improve it. In that case, you should compare the method in the exam to the one you've learned and see what's different.

JAMES: For example, they may give you a step-by-step method that doesn't mention insulating the block. In that case, the improvement will be to insulate the block to minimise the loss of energy in the surroundings.

ELLIE: So, here are some key things you need to remember. The aim of the experiment is to find out the specific heat capacity of a sample of material.

Two, during the practical, you need to record the temperature change, current and mass of the aluminium block.

And finally, one of the potential hazards of this practical is accidentally burning yourself. You can avoid this by not touching the heater when it's on and positioning the apparatus away from the edge of your bench.

JAMES: You'll learn more about this practical when you're in the class, but be sure to pay attention and make notes on everything that we mentioned here when it comes to practicing that experiment.

ELLIE: And, again, don't forget to stay safe and never touch a heater when in use.

So those are some of the key things you need to know for your practical investigation. In the next episode, we're going to be talking about power, so stay tuned.

JAMES: You sound like you're excited about that one.

ELLIE: Yeah. Woo!

JAMES: Thank you for listening to Bitesize Physics. As always, if you found this helpful, you can of course go back and listen again, make some notes along the way and come back here whenever you want to revise.

ELLIE: There's also so many resources available on the BBC Bitesize website, so be sure to check it out.

BOTH: Bye!

JAMES: Hello and welcome to the BBC Bitesize Physics podcast.

ELLIE: The series designed to help you tackle your GCSE in Physics and combined science.

JAMES: I'm James Stewart, I'm a climate science expert and TV presenter.

ELLIE: And I'm Ellie Hurer, a bioscience PhD researcher.

JAMES: And today we're going to be talking about power, how to calculate it and compare how much power different electrical devices use. Let us begin.

Ellie, if you could have any superpower in the world, what would it be?

ELLIE: Hmm, I think probably teleportation. Could you imagine being able to blink and go from London to, you know, the Amazon rainforest?

JAMES: Oh, wouldn't that be amazing? I think I would probably choose time travel. I'd love to go back in history and see like the first thing humans created or hang out with my great-great-great-grandfather, stuff like that.

But I didn't ask you that question because we're doing a spin-off show about superheroes. I asked you that because in this episode we are talking about power and to do that let's start with a scientific definition of power.

So power is the rate at which energy is transferred or the rate at which work is done. That means that the more powerful a device is, the more energy is transferred, or more work is done, each second.

ELLIE: To calculate power, you need a certain formula, so grab your pen and paper because you'll want to write this down.

So, power equals energy transferred, divided by time. So, let me repeat that with the units. Power, which is measured in watts, equals energy transferred, which is measured in joules, divided by time, which is measured in seconds. This means that an energy transfer of one joule per second is equal to one watt.

JAMES: If you want to learn more about power and energy transfer, be sure to listen to the energy transfer episode of our Bitesize Physics electricity series.

ELLIE: Yes, definitely go back and look at that. Right, so let's look at an example. So James, imagine it's a really hot summer's day so you buy an electric fan.

JAMES: The electric fan transfers 3,000 joules of energy in one minute. So how would you calculate the power of the fan if the equation to calculate the power is: power equals energy transferred divided by time.

ELLIE: If you missed a measurement or the equation, be sure to rewind, but we'll give you a few moments to pause, write that down and calculate it.

JAMES: Okay so to calculate the power rating of the fan, you would divide 3,000 joules by 60 seconds to get the answer, 50 watts.

ELLIE: What?

JAMES: Wahey. Therefore, the power rating of the fan is 50 watts. And you can often find the power rating of an appliance on a label, handily attached to its wires.

ELLIE: But, there's also another equation you can use to calculate power. So, let's grab your pen and paper. Okay, so power equals work done, divided by time. Let me repeat that with the units. Power, which is measured in watts, equals work done, which is measured in joules, divided by time, which is measured in seconds.

JAMES: Yeah, the main difference between those is instead of talking about energy transferred, we talk about work done. And to learn more about work done, be sure to listen to the work done episode of our BBC Bitesize Physics series on forces.

ELLIE: Let's look at another example. Imagine you're at a construction site and you're watching two different electric motors lift weights.

They both lift a 2 Newton weight by 10 metres. Motor one does it in 5 seconds, whereas motor two does it in 10 seconds.

JAMES: So to calculate how much energy they use, you would use the equation work done equals force multiplied by distance. So in this case, you multiply 2 newtons by 10 metres to get the answer 20 joules. But, how would we calculate how powerful each motor is?

ELLIE: Well, the equation for power is: power equals work done divided by time. So, I'm going to give you a few seconds to try and calculate the power of motor one and two using the equation.

JAMES: To calculate the power of motor one, you would divide its work done, which is 20 joules, by the time it takes, that was 5 seconds, to come up with the answer, 4 watts. And then to calculate the power of motor two, you would divide its work done, which was 20 joules, by its time, 10 seconds, to come up with the answer, 2 watts. That calculation would help you to understand why they both lift the same weight, but do it at different rates, because motor one is twice as powerful. Yeah, so if you need to move house and do some heavy lifting to get your furniture moved around, you'd probably use motor one to help you do that, otherwise you'd be very tired.

Let me just recap some of the key facts we learned today. So firstly, power is the rate at which energy is transferred or the rate at which work is done.

Secondly, the first equation to calculate power is: power equals energy transferred, divided by time. And the second equation to calculate power is: power equals work done, divided by time.

And finally, power is measured in watts. Work done is measured in joules. And time is measured in seconds.

ELLIE: So that's our introduction to power. In this next episode, we're going to be talking about the conservation and dissipation of energy, which is how it's used and wasted.

JAMES: Thank you for listening to Bitesize Physics. If you found this helpful, and I hope you did, go back and please listen again, make some notes as you go along the way, and always come back here whenever you want to revise from.

ELLIE: There's also a lot more resources available on the BBC Bitesize website, so be sure to check it out.

BOTH: Bye!

ELLIE: Hello and welcome to the BBC Bitesize Physics podcast.

JAMES: The series designed to help you tackle your GCSE in Physics and combined science. I'm James Stewart, I'm a climate science expert and TV presenter.

ELLIE: And I'm Ellie Hurer, a bioscience PhD researcher.

JAMES: And today we're going to be talking about the conservation and dissipation of energy and how to calculate it.

ELLIE: We started talking about energy transfers back in episode one of the series, so if you want to get a fuller picture, I'd recommend going back and listening to that first. But if you already have, let's begin!

JAMES: Ellie, there is one fundamental idea you need to know when it comes to energy. We've mentioned it a few times in this series and in other episodes of the podcast.

So, can you finish the sentence for me? Energy cannot be created…

ELLIE: Or destroyed – energy can be transferred usefully, stored or dissipated. And just as a reminder, ‘dissipated’ means it is wasted, usually by being lost to the surroundings.

JAMES: Yeah, that statement that energy cannot be created or destroyed has a name. It's called the law of conservation of energy. So that means when you toast a slice of bread, for example, and transfer the electric energy store into the thermal energy store of the heating element inside the toaster, that energy isn't being created or destroyed, it's just being transferred.

ELLIE: But how does that energy transfer change when it happens in a closed system like a slow cooker?

JAMES: Well in a closed system, energy is only transferred within that system. So while the electric energy of the plug is transferred into the thermal energy store of the slow cooker, there is no net change to the total energy of the whole system.

ELLIE: But even though there is no net change in the total energy, some of the energy is transferred in a non-useful way. For example, in heating the casing of the cooker rather than the food inside it.

JAMES: Have you ever been doing homework on a laptop and then suddenly it feels like your laptop is getting too hot? Put your clothes in the washing machine and gotten distracted by just how much noise it's making?

ELLIE: Well, that's because in all system changes, some energy is dissipated, which means it's wasted. When energy is transferred, some of it is stored in less useful ways. So let's talk through a few examples.

JAMES: When you drive a car, you convert some of the energy in the chemical energy store of the fuel into the kinetic energy store of the car, which is why it moves. But, some of that energy is dissipated. Any ideas how? I'll give you a few moments to think about that one.

One of the ways energy is dissipated in a car is through the way a car also transfers energy to the thermal energy store of the air particles in the surroundings, through the engine and the gas that comes out of the exhaust.

ELLIE: When you use a blender to make a smoothie, you transfer energy from the electrical energy store into the kinetic energy store of the blades of the blender. But some of that energy is dissipated here too. Can you guess how? I'll give you a few moments to think.

So, in a blender, some of that energy is dissipated because the blender converts some of that energy into sound waves.

JAMES: It does a very good job because blenders are so loud.

ELLIE: So loud.

JAMES: Unnecessarily so.

ELLIE: Yeah.

JAMES: And one final example, when you start a fire with wood to keep you warm, like on a cold winter's day, you transfer energy from the chemical energy store of that wood into the thermal energy store. But some of that energy is dissipated because it becomes light energy which you might not need if you were starting the fire in the middle of the day, for example.

ELLIE: So a lot of that energy is wasted during energy transfers, but does it have to be that way?

JAMES: Well, we can reduce the amount of energy wasted is the good news. So as the world becomes more environmentally friendly, people are always coming up with more energy efficient ways of building things. Especially when it comes to dissipated thermal energy. For example, an energy efficient light bulb is great.

ELLIE: When you switch on a light bulb, it gives you light energy. However, in the past, if you were to touch a bulb, which I really don't recommend you do, the old-fashioned bulbs used to get very, very hot.

JAMES: But that thermal energy is wasted because you don't need your light bulb to warm up the room. So inventors have created energy efficient light bulbs that transfer more of the energy usefully, so less energy is wasted as heat to the surroundings.

ELLIE: The higher the thermal conductivity of a material, the higher the rate of energy transfer by conduction across the material. So, the better a material is at conducting heat, the more energy that is transferred across it.

JAMES: Yeah, a laptop is a really good example of this. So, let's say you're working on a school project and you're using loads of tabs and different apps to do that. The laptop is going to get hotter. This is waste thermal energy. And some of the components inside are made of metal, which more easily conduct heat, so more heat energy is lost through them. And even though your laptop doesn't need to be hot to work, it is still heating up.

But knowing that fact, that the higher the thermal conductivity of a material the higher the rate of energy transfer by conduction, can help us create more energy efficient buildings.

ELLIE: We've got to insulate a building with materials that have a low thermal conductivity.

JAMES: So Ellie, if you could build your dream house, what materials would you use to build it?

ELLIE: Hmm, probably a combination of things like bricks, glass and wood. You know, like, most buildings are made of.

JAMES: Yeah, they are. And for a very specific reason, to manage different temperatures. So, no matter where Ellie's dream house is built, it can handle it. If you were to build a house with copper walls, it would get very, very hot in the summer and incredibly cold in the winter. Because copper has a high thermal conductivity.

ELLIE: And that's why we build houses with materials like brick and wood. Because they are poor thermal conductors. And the thicker the material used, the less heat that will be conducted through it.

JAMES: And some houses even have layers of fibre between the bricks called cavity wall insulation to insulate them even more. That way the walls of the house keep heat in and stop it from being able to conduct through the walls as easily.

ELLIE: So, when it comes to energy transfers, there are lots of ways we can build buildings and products to make them more energy efficient and reduce the amount of waste they release into the environment.

JAMES: But if you want to learn more about insulation and the different ways it's being used to insulate buildings and other structures, head to the BBC Bitesize page to learn more.

ELLIE: But before we go, let me recap the three key takeaways we heard today. So, the first key point is: energy can be transferred usefully, stored or dissipated, but it cannot be created or destroyed.

And in all system changes, energy is dissipated so that it is stored in less useful ways. This energy is often described as being wasted.

And finally, the higher the thermal conductivity of a material, the higher the rate of energy transfer by conduction across the material. Okay, so now you understand the basics of conservation and dissipation of energy. In the next episode of Bitesize Physics, we're going to explore efficiency and how to calculate it.

JAMES: Thank you for listening to Bitesize Physics. If you found this helpful, please go back and listen again. And of course, make some notes as you go along and always come back here whenever you need to revise.

BOTH: Bye!

JAMES: Hello and welcome to the BBC Bitesize Physics podcast.

ELLIE: The series designed to help you tackle your GCSE in Physics and combined science.

JAMES: I'm James Stewart, I'm a climate science expert and TV presenter.

ELLIE: And I'm Ellie Hurer, a bioscience PhD researcher. And let's get started.

JAMES: So in the last episode, we touched on the topic of efficiency. If you haven't listened to that episode 6, last episode, be sure to head back there because it has some really helpful information you'll need to understand just what we're talking about today.

Efficiency is how well an object achieves maximum productivity with minimum waste. So, for example, a lightbulb that is supposed to light up a room, that instead makes it really hot, isn't very efficient because it's wasting heat energy. This is why we have energy-efficient light bulbs.

To calculate how efficient an energy transfer is, you need to understand a key equation.

So, grab your pen and paper if it's handy.

Efficiency equals useful output energy transfer, divided by total input energy transfer.

ELLIE: So let me give you that equation again this time with the units of measurement that we need to use. So, efficiency equals useful output energy transfer, which is measured in joules, divided by total input energy transfer, which is also measured in joules.

JAMES: Handy. And it's important to know that efficiency doesn't have a unit. Instead, it's given as a decimal or as a percentage. So, let's use a lightbulb as an example. Let's imagine you just bought a new lamp for your bedside table and you had to pop out to the supermarket and buy yourself a lightbulb.

ELLIE: So, if the lightbulb is supplied with 200 joules of energy and only 28 joules of that energy is used to actually light it up, how would you work out how efficient the lightbulb is?

JAMES: Well, you would divide 28 joules, that's the useful output energy transfer, by 200 joules, the title input energy transfer, to get the answer 0.14. So the bulbs efficiency is just 0.14. To calculate the percentage of efficiency, you multiply efficiency by 100, so 0.14 multiplied by 100 - therefore, the energy percentage efficiency is 14%.

ELLIE: Most of the energy isn't used to light up a room. It's dissipated, which means it's wasted, by being transferred into other energy stores like the thermal energy store of the surrounding air particles. This means that the light bulb is not very efficient.

JAMES: Yeah, so basically you need to get a better bulb for your lamp, is what we're saying.

ELLIE: Buy a better bulb.

You can also measure efficiency with a similar equation. So, it's time to grab your pen and paper again. Right, so, efficiency equals useful power output, which is measured in watts, divided by total power input, which is also measured in watts.

JAMES: Let's try another example. So imagine it's your best mate's birthday and you decided to make them a cake. You're a very good friend. So you reach into your cupboard, and you grab your mixer.

That mixer had an input of 400 watts of power, but it only used 110 watts of that power to actually mix the cake batter. So how efficient is that mixer?

ELLIE: I'll give you a second to try and calculate that by yourself. And just as a reminder, the equation is: efficiency equals useful power output, which is measured in watts, divided by total power input, which is also measured in watts.

JAMES: So, to calculate the mixer's efficiency, you would divide 110 by 400 to get the answer of 0.275. If you were to multiply that by 100, you would get the percentage efficiency of 27.5%, which means, again, that mixer isn't really that efficient.

ELLIE: So maybe you should just use a wooden spoon to make the cake batter instead. That way, you'll save electrical energy.

JAMES: That’s what I get told to do at home, yeah, I will do.

ELLIE: Also, it's useful to know that efficiency can never have a value of more than one if the answer is being given as a decimal, or more than a hundred if the answer is being given as a percentage. So, if you ever calculate and get more than that, you'll know that you've gotten the wrong answer and you need to go back and try again, basically.

JAMES: It's a good tip though, that one.

So the key question, I guess, Ellie, is how can you increase the efficiency of an energy transfer then?

ELLIE: Yeah, there are so many ways to do that, but if we're talking about houses, the most efficient is probably insulation. One great way to tell which house on the street has the best insulation is to look at the roof when it snows.

JAMES: Yeah, if the roof on one house has lots of snow on it, that probably means that it's better insulated and that the house has been built with materials or been insulated in a way that keeps the heat in because the snow melts more slowly.

ELLIE: Whereas, the house with less snow on its roof is probably less insulated, which means the heat from inside the house is warming up the snow.

People can insulate their homes using things like double-glazed windows, cavity walls, carpets and curtains and loft insulation.

JAMES: Yeah, and this doesn't just apply to homes as well. Light bulbs made of thicker glass waste less heat energy, and even serving dishes made with thicker, less conductive materials keeps food warmer for longer.

ELLIE: And when it comes to designing products or mechanical equipment, lubricating the different parts will reduce friction. This means there will be less wasted thermal energy and the item will be more efficient.

JAMES: So the next time you go shopping for an appliance or an electric item, have a look at its energy efficiency. You'll see it in a whole new way. It's usually written out on a label covered with red, yellow, orange and green arrows.

ELLIE: Before we go, I have a question for you. What household appliance do you think is the most efficient? I'll give you a minute to think.

JAMES: The answer is…

ELLIE: Duh, duh, duh, duh, duh…

JAMES: A heater!

ELLIE: Woo!

JAMES: Woo! Very handy. Because its job is actually to transfer energy to the thermal energy stores of itself and the air around it which is really smart. There's very little wastage, if any at all, really.

ELLIE: So, I think the key takeaway here is to get yourself a heater.

JAMES: Yes, I think so. Job done.

ELLIE: Job done.

Before we finish this episode, let's recap the three key takeaways. The first equation to calculate efficiency is: efficiency equals useful output energy transfer, divided by total input energy transfer.

The second equation to calculate efficiency is: efficiency equals useful power output, divided by total power input.

And finally, two methods of increasing efficiency are: insulation and lubrication.

JAMES: So that's a great introduction to efficiency and how to calculate it. It might even help you pick out the best light bulbs and the devices you need when you go shopping next.

ELLIE: Thank you for listening to BBC Bitesize Physics. If you found this helpful, go back and listen again and make some notes so you can come back to this any time when you revise.

BOTH: Bye!

ELLIE: Hello and welcome to the BBC Bitesize Physics podcast.

JAMES: The series designed to help you tackle your GCSE in physics and combined science. I'm James Stewart, I'm a climate science expert and TV presenter.

ELLIE: And I'm Ellie Hurer, a bioscience PhD researcher.

JAMES: And this is the eighth and final, sadly, episode of our series on energy. If you haven't listened to the other seven, where have you been? Of course, you can go back, pause the episode, and come back to episode one and listen all the way through and get the most out of the series.

ELLIE: Alright, and with that, let's kick off our final episode where we'll be talking about renewable and non-renewable energy resources.

JAMES: This is a bit of me, this.

ELLIE: Yeah, this is your expertise.

JAMES: Yeah, I love a bit of non-renewables and renewables. Just so you know, while we're going to cover some of the key points in this one, we can't cover everything in one episode. We wish we could. So do be sure to head to the BBC Bitesize page and read the resources your school gives you, so you're fully equipped. Okay, let's begin.

ELLIE: Okay, so we've spent this entire series talking about energy and how we use it, but we haven't talked about where that energy actually comes from.

JAMES: Well, the main energy resources we use on earth are fossil fuels - things like coal, oil and gas, as well as other fuels like wind, hydroelectricity, nuclear fuel, biofuel, geothermal energy, the tides, the sun and water waves.

So, some energy is renewable, which means that it can be replenished as it's used. ‘Replenished’ means that you can restore that energy resource because it's always been created naturally.

ELLIE: For example, wind energy that's used to turn wind turbines and the energy we get from the sun that's used in solar panels.

JAMES: Yeah, whereas other types of energy are non-renewable. For example, nuclear fuel and the three fossil fuels, which are coal, oil and gas. That means that once they are used, we can't naturally recreate them at a pace quick enough to keep up with the human consumption. And that's sort of the problem.

As humans, a lot of the energy we use is non-renewable. Yeah, imagine a busy city at rush hour, there’s lots of the cars on the streets that are powered by petrol and diesel. Now those aren’t renewable and they do leave pollution in the air.

Yeah, they also, unfortunately, create high levels of carbon dioxide in the atmosphere which warms the planet and can cause changes in our weather systems, which, of course, is not good for any of us. Petrol and diesel are fossil fuels. They're made from crude oil, which is found in the Earth's crust. So once all that crude oil's been used up, we can't replenish it because there's a limited amount of it in the world. It's finite.

OK, I know what you’re thinking – if they're not renewable, they're not good for the environment and we’ll eventually run out of them, why do we still use them?

It’s a great question. And simply, it’s because we've been using them for centuries. And a lot of technology we use from things like our cars to heating in our homes was designed for them. So whilst the UK's energy does come from different sources, a lot of it comes from fossil fuels.

As we all become more aware of the effect we're having on the planet, people have started to redesign technology to use power in more sustainably. Scientists, just like Ellie and myself, and environmental activists have campaigned and created more sustainable ways to supply and use energy. Electric cars, lamp posts, fuel by solar power, cool stuff like that, wind turbines in the countryside are used to power businesses and factories.

But there are a lot of other factors to consider that make it difficult to switch to more sustainable options. For example, the costs associated with things like research and development and the fact that different countries need to come together and set sustainability targets that they agree on to use more renewable energy resources.

Also, there are other practical factors to think about. For example, the limited reliability of some renewable fuels compared to fossil fuels. For example, solar energy, well, you can't really rely on it in the winter.

ELLIE: We really do still have a long way to go, but more people are aware of the renewable alternatives they could use. And hopefully one day, using renewable energy will be just as easy as using non-renewable energy.

JAMES: Yeah, for example, in the UK, there will eventually be a ban on selling new petrol and diesel cars as the country pushes towards more hybrid and electric cars.

ELLIE: But you don't have to be a politician or have the money to buy an electric car to make a difference. You can try small swaps to make the way you use energy a little more sustainable too.

JAMES: Yeah, you could try walking or riding a bike to school instead of taking the bus. Or you could ask your school to use LED light bulbs instead of incandescent light bulbs in the canteen, for example.

ELLIE: You know, even if it's just a small change, everything you can do to be more environmentally friendly has a positive impact. So, take a moment to think about what you can do to make a difference.

JAMES: Yeah, and sometimes you feel like, I'm just one person, what difference can I actually make? A huge one!

ELLIE: Yeah.

JAMES: That is the answer. So, get cracking. Small differences, good way to start. Alright, let's recap the three key takeaways from today's episode then.

So firstly, some energy resources are renewable. That would be things like solar, wind and geothermal energy.

Secondly, other energy sources are non-renewable - things like coal, oil and gas. But we use them because they can sometimes be more reliable than existing tech. Although, that might change as tech catches up.

And lastly, non-renewable energy sources harm the environment, but more technology is being developed to make the products we use more sustainable.

ELLIE: And with that comes the end of our eight-part series all about energy.

JAMES: Oh, sad face. We really hope you found it helpful and if you didn't get the chance to listen to all these episodes, please do go back and really get stuck into them. There's some good stuff in there.

ELLIE: And again, thank you guys for listening to BBC Bitesize Physics. If you found this helpful, go back and listen again and make some notes so that you can come back to them when you revise.

JAMES: Whilst you're in the BBC sounds app, there's also the Bitesize Study Support podcast, which is full of tips to help you stay focused during revision and get the best out of your exam.

ELLIE: Good luck with all your exams, guys. You're gonna smash it.

JAMES: Yeah, and we'll see you again. Thanks for listening.

ELLIE: Thank you.

BOTH: Bye!