Lesson video

- Hello, I'm Ms. Holsmith and today I'm gonna be your physics teacher.

Now, you will need a calculator for this lesson, as later on we're gonna be doing some calculations.

Let's get started.

Today's lesson is all about conduction.

We're gonna explain the process of conduction and look at an investigation into the thermal conductivity of some different metals.

This lesson is part of the energy topic within science.

First, we need to have a look at the keywords that we're gonna use in this lesson.

Temperature is how hot a substance is, and it's measured in degrees Celsius, and that is represented by a little o superscript and a capital C.

Solids have a regular arrangement of particles, and as you can see from the diagram there, the particles are arranged in a fixed pattern.

An insulator is a material that is a poor conductor of thermal energy, which means that they can't conduct thermal energy very well.

This lesson has three learning cycles, temperature and heat, understanding conduction, and investigating conduction.

We're gonna start off by looking at temperature and heat.

Temperature is a measure of how hot something is.

So you'll probably have heard of temperature being spoken about when people might be talking about how hot they need to put the oven to cook some food.

Temperature is measured using a thermometer.

Thermometers can be analogue, so you might have seen these at school where it's a glass rod with some mercury inside that will rise or fall depending on the temperature.

Or thermometers can sometimes be digital, which is where you have a probe and a screen that actually tells you the temperature of the substance that you're measuring.

Digital thermometers are generally a bit more accurate than analogue thermometers, as the analogue thermometers that are made of glass can sometimes be hard to read.

Temperature is measured in degrees Celsius, and the way that we write this unit is to do a little superscript o and a capital C.

Heat is a measure of the energy in the thermal energy store of an object.

So because heat is a measure of energy, it is therefore measured in joules, and we can represent joules with a capital J.

Heat is a measure of the amount of energy in an object's thermal energy store.

The thermal energy store of an object depends on two things, the number of particles in the object and the energy of the particles.

The sparks from a sparkler have really, really high temperature, but a relatively low thermal energy, 'cause they consist of very few particles.

So even though the tip of a sparkler will be really, really hot and it might even burn your hand if you touch the tip of it, its thermal energy overall is actually quite low because it's such a small area that's hot.

So why does the water in a warm bath have more thermal energy than sparks from a sparkler? Even though the sparkler can have a temperature of around 1,000 degrees Celsius, which sounds really, really hot, its thermal energy is low because the actual number of particles at that temperature is quite a small number in comparison to the bath.

The bath has a temperature of 50 degrees Celsius, which is a lot lower temperature than the sparkler, but there are loads and loads of particles in a bath so its thermal energy is high.

Because there are many more particles in the bath of water, it has more thermal energy than the sparkler.

Let's check your understanding of heat and temperature.

Heat is a measure of? Excellent.

It's the energy in the thermal energy store of an object.

And remember, I said because it's energy, it's actually measured in joules.

What unit is temperature measured in? Excellent, it's degrees Celsius.

It can't have been joules, because that's a measure of energy.

Now it's your turn to practise your knowledge of heat and temperature.

Draw lines to match the information about heat and temperature.

You need to match the description and also match it up to the unit they are measured in.

Pause the video now and press play when you're ready to go through the answers.

Okay, let's go through the answers.

So, heat is a measure of the energy in the thermal energy store of an object, and we measure this in joules.

Any type of energy store is measured in joules, so heat or thermal energy is measured in joules.

Temperature is a way to measure how hot or cold something is and it is measured in degrees Celsius.

Remember we said we can use a thermometer to measure temperature, and that would tell us if something is cold or hot.

And room temperature would be around 22 degrees Celsius.

Really great job if you got those correct.

Which beaker has the highest heat, or thermal energy? And explain your answer.

Pause the video now, have a go at the task, and then press play when you're ready to see the answer.

Okay, so beaker C has the highest thermal energy.

Although the water in all the beakers was reading the same temperature, 20 degrees Celsius, the particles are all moving in the same energy.

However, because there's more water, so more particles in beaker C, it's going to have more thermal energy.

So there was more thermal energy stored in beaker C than beaker A or B.

Beaker B would therefore have the lowest amount of thermal energy.

Really well done if you figured that one out.

It was really tricky, because the temperatures are the same.

So it's a really common mistake to think that they all have the same amount of thermal energy.

But remember, thermal energy also depends on the amount of particles.

Okay, we are now gonna move on to the second learning cycle in this lesson, understanding conduction.

Thermal energy is transferred from hotter regions to colder regions.

So something that is hotter would transfer energy to something that's colder.

The bigger the difference in the temperature between the hotter and colder region, the faster energy transfer will occur.

So if I had a very, very hot object next to a cooler object, that cooler object would heat up more quickly than if the hotter object was only a little bit hotter than the cold object.

Here's an example using some different temperatures.

If I had two different objects, one that was 90 degrees Celsius and one that was 20 degrees Celsius, this would have quite a fast energy transfer, because there's quite a big difference between those two temperatures, 70 degrees celsius difference.

However, if I had two different objects that only had a 10 degree Celsius difference, so between 90 degrees Celsius and 80 degrees Celsius, this would be a much slower energy transfer because there's not as big a difference in temperature.

In solids, energy is transferred by conduction.

Metals are good thermal conductors.

Non-metals are poor thermal conductors.

We can call it an insulator.

Because metals are good thermal conductors, they're often used in things like saucepans or frying pans or in cooking because we want them to get hot.

In comparison, we would use non-metals for things that we don't necessarily want to transfer thermal energy.

So how does conduction occur? Here there's a diagram of the solid particles in a metal bar.

We can see that all the particles have a uniform arrangement in a fixed pattern.

When heat is applied to the metal bar, watch what happens.

Heating the particles transferred energy to them, which caused them to gain energy in their kinetic energy store.

Therefore, they will vibrate more.

When they vibrate more, they will then collide with nearby particles, because the particles in the solid are so close together.

This transfers energy between particles and causes the next particle to vibrate as well.

As we saw from that diagram, as the particles vibrated they passed on that energy throughout all the particles as those vibrations caused collisions.

Let's check your knowledge now of conduction.

Which one of these objects will conduct thermal energy the fastest? Excellent, it's going to be the metal fork.

Remember we said that metal forks or metals are really good conductors of thermal energy.

A wooden spoon or a plastic knife are non-metals, so they are not good conductors of thermal energy.

We'd refer to them as insulators.

True or false? Plastic is a better conductor than metal.

This is false.

Plastic is a poor thermal conductor.

It's a non-metal, and generally non-metals are pretty poor at conducting thermal energy.

Well done if you've got that one right.

You're now gonna practise your understanding of conduction.

Have a go at the tasks on the screen, pause the video, and press play when you're ready to go through the answers.

Okay, let's have a look at the answers.

Describe the process of conduction.

Heating particles transfers energy to them, causing them to gain energy in their kinetic energy store and vibrate more.

These vibrating particles then collide with nearby particles, because in a solid the particles are really close together.

This transfers energy and causes those particles to vibrate more as well.

Explain why using a metal mug to drink hot drinks from would not be a good idea.

Use ideas about conduction in your answer.

So before we go through this answer, let's just remind ourself that metals are really good conductors of thermal energy.

Because they're good conductors of thermal energy, they won't make a good drinking mug, because that means the metal would conduct thermal energy from the drink and become really hot, which could then burn your lips.

It's a bit of a misconception that people think because something's a good thermal conductor, we'd want it to hold something hot.

Well, that's if we want the thing to get hot, such as a radiator.

But in the instance of a mug of hot drink, we don't actually want the mug itself to get hot.

If anything, we'd want the drink to be insulated so that it stays hot.

We don't want the thermal energy to be transferred away from the drink.

Excellent job if you got those two questions correct, particularly that second one with the metal mug was really difficult and challenging, so really well done if you applied your knowledge correctly.

We're now gonna move on to the final learning cycle in this lesson, investigating conduction.

We can carry out an investigation into which metal is the best conductor of thermal energy.

Take a look at the diagram.

We have a Bunsen burner that is heating up the end of four different rods.

We've got an iron rod, a copper rod, a brass rod, and an aluminium rod.

At the end of each rod is a drawing pin attached with Vaseline.

The metal rods are all on top of a tripod stand so that the Bunsen burner flame can touch them.

Have a think about why the drawing pins are attached to the metal rods by Vaseline.

How will you know which metal rod is the best thermal conductor? And what will you need to control to get valid results? So in this investigation, the Bunsen burner is going to heat up those metal rods, it's going to transfer thermal energy to them.

Conduction will then occur down the metal rod.

The particles in each rod will vibrate more and pass on energy to the next particles.

The drawing pins at the end are attached to the metal rods with Vaseline because when the Vaseline melts, the drawing pin will fall off the end of the rod, and this will tell us how long it took the thermal energy to be transferred across the rod compared to the other rods.

So the reason that we've used Vaseline is because this will melt with only a relatively small increase in thermal energy.

We'll know which metal is the best thermal conductor because the drawing pin that falls off the quickest would've had the thermal energy transferred more quickly along the rod.

If thermal energy is transferred more quickly, that means that that metal was a better thermal conductor.

So the drawing pin that falls off last would be on the metal that is the worst thermal conductor.

In order to get valid results, we would need to control a few factors.

Firstly, we would need the length and the thickness of each of the rods to be the same.

We want to change the metal of the rod, so we need to ensure that the length and thickness are the same in order to make sure it's a valid test.

We'll also want to make sure that the ends of the metal rods are all in the Bunsen burner flame.

If one of them was pointed out to the side and not in the flame properly, this wouldn't be a valid test because it wouldn't have the same amount of thermal energy transferred to it as the other rods.

Now have think about what is the independent variable in this investigation? What is the dependent variable? And how could we make sure we get accurate results? So in this investigation, the independent variable is the type of metal used for each rod.

That's what we're changing throughout this investigation.

The dependent variable is the amount of time that it takes each drawing pin to fall off the rod, and therefore we're measuring the thermal conductivity, or how good that metal is at conducting thermal energy.

We can get accurate results by making sure that we control all the control variables we spoke about before, but also repeating the test again.

We may want to then calculate a mean time for each pin to drop off.

The more repeats we do, the more accurate our results will be.

It's also important during this investigation that we consider some different health and safety factors.

For example, when we're using Bunsen burners which have an open flame, we'd want to make sure that our hair was tied back and the Bunsen burner was on a heatproof mat.

We would also need to be really careful about touching the metal rods once the investigation is finished.

This is because the metal rods could have a really high temperature which could burn our hands.

Have a look at the data on the screen from an investigation that was repeated three times.

The data has been recorded for each of the four types of metal rod, steel, copper, brass, and aluminium.

And for each rod we have three different times that it took for the pin to fall.

We need to calculate a mean time for each metal.

To calculate a mean, we need to add all the values together and divide by the number of values there were.

In this example for the steel rod, we need to add 43, 46, and 46 seconds.

That gives me a total of 135.

I then need to divide 135 by 3, because that's how many values there were, to give me a mean time for the pin to fall.

That gives me a mean time of 45 seconds.

And I can pop that mean in the table.

Now it's your turn to practise calculating the means for each metal.

Remember, you need to add up the three values and divide it by three.

Pause the video now, have a go at that question, and then press play when you're ready to go through the answers.

Okay, let's check your calculations.

So for copper we had to add 29, 33, and 28 seconds.

This gave me a total of 90, divided by 3 was a mean of 30 seconds.

For brass, 34, add 35, add 36, gives me 105.

Divided by 3 is 35.

Finally, for aluminium, 41, 42, and 37 gives me 120.

Divided by 3 gives me 40 seconds.

Well done if you calculated the means correctly.

Your next task is to plot the data from the table as a bar chart.

On the y-axis Is the mean time taken for the pin to fall.

You'll need to add the different types of metal rod to the x-axis and draw bars accordingly.

Pause the video now and press play when you're ready to check your bar chart.

Remember to use a pencil and ruler.

If you make a mistake, you'll be able to change it easily.

Firstly, I've added labels to the axes, the mean time taken for the pin to fall in seconds on the y-axis, and the type of metal rod on the x-axis.

I've then drawn on the four bars for steel, copper, brass, and aluminium.

You'll notice that the height of each bar goes up to the mean time it took for the pin to fall off that particular metal.

I've also left a gap between each bar.

Excellent job if your bar chart looked like this.

Your next task is to analyse that data from your bar chart.

Have a go at these questions using the bar chart to help you determine the answers.

Press pause on the video now and then play when you're ready to go through the answers.

Let's check our answers.

Starting with the metal with the highest thermal conductivity, sort the metals into order of thermal conductivity.

So this means how well the metal can conduct thermal energy.

Copper had the highest thermal conductivity.

This is because it had the shortest time for the drawing pin to fall off.

After this it was brass, then aluminium, and then steel.

Steel had the longest time for the drawing pin to fall off, so therefore it had the lowest thermal conductivity.

Of the metals tested, which is the best one to use to make saucepans? Explain your answer.

We would want to use copper to make saucepans from because it has the highest thermal conductivity.

This means it transfers thermal energy the quickest, so it'll cook our food really quickly.

On TV, you might have seen chefs using copper-based saucepans to cook food.

This is 'cause that's the best metal to use for saucepans.

Really good job if you managed to work that out.

It was really tricky to be able to apply your knowledge of thermal conductivity to a real-life scenario, so well done.

Let's finish off with a summary of today's lesson on conduction.

When thermal energy is transferred from a hotter region to a colder region by particles, this is conduction.

Conduction occurs fastest in solids, and this is because the particles are very close together so they can pass on thermal energy really well.

Metals are excellent examples of thermal conductors.

We can investigate conduction by timing how long it takes drawing pins to fall off different metal rods when the metal rods were heated.

The faster the time it took for the drawing pin to fall off, the better the conductor.

Thanks for joining me on today's lesson on conduction.

See you next time!.