Thermal Physics

Question 1

Define heat energy.

Answer 1

Heat energy is the total amount of energy of all of the particles in a substance

Question 2

Define temperature.

Answer 2

The temperature of an object is proportional to the average kinetic energy of the particles. We cannot sense temperature, only heat.

Question 3

What are the different types of burn?

Answer 3

-Heat burn e.g. touching a flame
-Friction burn e.g. This is when cells are rubbed off by friction
-Cold burn e.g. This is when ice crystals grow in our cells and then burst our cells

Question 4

What do we mean when we say something is hot?

Answer 4

It has fast moving particles

Question 5

What is the difference between our hand and a hot object?

Answer 5

-The hand has slower moving particles whereas the object has faster moving particles

Question 6

What happens when our hand touches a hot object?

Answer 6

-Energy is transferred and our particles start to move more quickly. Heat always transfers from a hot object to a colder one.

Question 7

NEVER SAY “THE PARTICLES EXPAND”

Answer 7

-Instead, say the particles move further apart and need to take up more space.

Question 8

Cell membranes can be burst by expanding contents.

Answer 8

-When water in cells gets hot, it expands. If it expands too much. the cell bursts and we call this a burn.

Question 9

Structuring your thinking?

Answer 9

i. What is the physics theory/equation/law
ii. How does that explain the phenomenon
iii. What is the consequence in tis context (how does this answer the question for THAT scenario)

Question 10

Particles getting hotter.

Answer 10

When something heats up, the particles move faster and need more space so the substance expands.

Question 11

Particles getting colder.

Answer 11

When something cools down, the particles move slower and need less space so the substance contracts.

Question 12

Trains may buckle on a hot day.

Answer 12

When the rails get hot on a sunny day the atoms vibrate more and take up more space. This makes the rails expand, but with nowhere to go they buckle. This may cause a crash as trains could come off the rails.

Question 13

Bridge road sections join the main road and are connected by the “finger expansion joint”

Answer 13

When the road gets hot on a sunny day, the atoms vibrate more and take up more space. This makes the road expand, but with a finger expansion joint the road can expand and close the gap so that the road does not buckle, This prevents damage to the roads.

Question 14

What do these hot air balloons have to do with thermal expansion?

Answer 14

When the air gets hot due to the burners the air particles move faster and take up more space. This makes the air in the balloon expand, becoming less dense and will start to float.

Question 15

Why is someone using a hairdryer on this stuck jar lid?

Answer 15

When the lid gets hot due to the hot air, the atoms vibrate more and take up more space. This makes the lid expand. The glass must also expand but it must expand less.

Question 16

Why do metals conduct heat well?

Answer 16

It’s the same as conducting electricity. Metals have lots of free electrons which when heated will spread down the metal, carrying their energy.​

Question 17

What do we call a poor conductor of electricity?

Answer 17

An insulator

Question 18

Define conduction?

Answer 18

Heat transfer due to contact between two objects.

Question 19

Does the Sun conduct heat to the Earth?

Answer 19

No it doesn’t. ​

Conduction requires transfer of energy from particle to particle. ​

As space is essentially empty, heat energy cannot conduct through space.

Question 20

Why is air a good insulator?

Answer 20

Air is a good insulator because in a gas the molecules are far apart making collisions rare so conduction through a gas is poor. ​

Question 21

Describe the motion of particles in a solid.

Answer 21

Particles vibrate around a fixed point

Question 22

Describe the motion of particles in a liquid.

Answer 22

Particles move around each other but still are close together

Question 23

Describe the motion of particles in a gas.

Answer 23

They move freely.

Question 24

What can our bodies do if we sense too much heat?

Answer 24

The body can send signals to move or increase sweating.

Question 25

How do we sense heat?

Answer 25

Thermoreceptors… never cells in our skin send electrical signals.

Question 26

What experiment showed that particles that we cannot see move?

Answer 26

-Brownian motion:
-Particles are in constant random motion (we see this due to the large particles i.e. pollen grains being battered around, changing direction at random)

Question 27

How can heat transfer by conduction be decreased?

Answer 27

-Using a better insulating substance
-Decreasing the area of a substance

Question 28

Which is safer: a rubber handle or a metal handle?

Answer 28

-Rubber handle
-It is the better insulator so will conduct less heat to the hand
-to prevent burning
-(full explanation why this is safest requires a mention of the risk)​

Question 29

Answering conduction questions.

Answer 29

When answering a heat transfer question, you must ask yourself the following.​

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Heat flows from a hot thing to a cold thing so which way is it going in this situation?​

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Do we want the heat to go this way? Explain.​

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If we do … how does something in the scenario make it work better?​

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If we don’t … how could we reduce heat flow?​

Question 30

Explain how the bird keeps warm in the snow

Answer 30

In the cold weather, heat will flow from the bird’s warmer body to the cooler surroundings. It would want to prevent this heat flow. Puffing out its feathers traps more air in between the feathers. Because air is a good insulator, this reduces heat loss. This means that the bird can stay warm in a cold environment.​

Question 31

Explain why this man is wearing thick clothing.

Answer 31

In the cold weather, heat will flow from the man’s warmer body to the cooler surroundings. He would want to prevent this heat flow. Wearing thick clothes traps air in between the layers. Because air is a good insulator, this reduces heat loss. This means that the man can stay warm in a cold environment.

Question 32

What will happen if you put a coat on a snowman on a sunny day?​

Answer 32

The snow is colder than the air, so heat will flow from the air to the snowman. Wearing a coat traps a layer air. Because air is a good insulator, this reduces heat flow. This means that snowman will stay colder for longer and not melt as quickly!​

Question 33

Describe how energy is transferred through a solid. Remember to name the process.

Answer 33

Conduction. Particles are vibrating around a fixed point. When they heat, they vibrate faster. They transfer energy to their neighbors as they are connected by forces/bonds.​

Question 34

What is SHC?

Answer 34

The specific heat capacity of a substance is the amount of energy needed to change the temperature of 1kg of the substance by 1oC.​

Question 35

Why is water useful in terms of SHC?

Answer 35

Water has a particularly high SHC, making it very useful for storing heat energy, and for transporting it, e.g. in central heating​

Question 36

Define a convection current.

Answer 36

A convection current is the path taken by rising hot fluids and sinking cold fluids.​

Question 37

Sentence stems to answer convection questions.

Answer 37

The fluid is warmed by….
This causes the fluid to become less dense
So it floats above the colder fluid
As it spreads around it loses energy and cools down
Becoming less dense
So it sinks back down
The cold fluid moves back towards the….

Question 38

In terms of thermal physics, explain why someone camping in winter would be warmer on an air mattress than directly on the ground. (3 marks)​

Answer 38

When sleeping on the ground, the energy flow would be from the person’s warmer body to the cooler ground. Someone camping in winter would want to prevent heat loss from the body. By sleeping on an air-filled mattress, the air acts as an insulator to reduce heat transfer. This would keep the camper warmer in winter.​

Question 39

Thinking steps for answering heat flow questions

Answer 39

Which way would energy flow? Do you want it to go this way?​

a. If yes: how does this scenario increase heat flow?​

    b. If no: how does this scenario reduce heat flow? ​

3. Link it back to the scenario​
4. Put it all together in a paragraph/full sentence dot-points.​

Question 40

Light is made when…

Answer 40

A charge accelerates

Question 41

Light is created when a charge accelerates because

Answer 41

A moving charge creates a moving electric field, and a moving electric field creates a moving magnetic field.​

The result is a self-propagating electro-magnetic wave, also known as light.

Question 42

How does light transfer energy?

Answer 42

It can be absorbed and thus it’s energy is transferred.

Question 43

Which has more heat energy, a lake at 10 degrees or a cup of coffee at 100 degrees?​

Answer 43

The lake… even though it is cooler the total heat energy from all of those particles (essentially their kinetic energy) will be greater than the total kinetic energy in the cup.​

Question 44

What are the two fixed points we mark on any thermometer?​

Answer 44

Freezing point of PURE water at SEA LEVEL​

Boiling point of PURE water at SEA LEVEL​

Question 45

What is the name for the process of putting the scale on a thermometer (or any measuring device)?​

Answer 45

Calibration

Question 46

How does a liquid in glass thermometer work?

Answer 46

Heating causes expansion of the liquid which will rise up the tube. Cooling leads to contraction and the liquid falls down the tube.

Question 47

What does this graph show between atmospheric pressure and temperature of gas particles?

Answer 47

Pressure of a gas = zero when the particles stop moving. This is the coldest temperature possible at -273oC​