+++++ S 33: Heat, Energy And Energy Transfer

Question 1

What is heat and what is it measured in?

Answer 1

Heat is a form of energy. It is measured in joules (J).

Question 2

What 3 main effects are from adding heat energy to a material?

Answer 2

It can cause the temperature of a substance to increase.
It can cause the material to expand.
It can change the state of a substance from solid to liquid or from liquid to gas.

Question 3

Explain the observations and conclusions of an experiment that shows that when heat energy is added to a substance, it expands.

Answer 3

To show that solids expand when heat energy is added and that they contract when they are cooled.
Observations:
When the ball is at room temperature, it passes through the ring.
When the ball is hot, it will not pass through the ring.
If the ball is cooled down, it will pass through again.
Conclusion:
When metals are heated they expand. When they are cooled they contract.

Question 4

Why does hot water crack thick glass?

Answer 4

Hot water can crack thick glass because the inside gets hot more quickly than the outside. The inside of the glass expands faster than the outside and the glass cracks.

Question 5

Explain the introduction, observations and conclusions of an experiment that shows that liquids expand when heat energy is added and that they contract when heat energy is lost.

Answer 5

Introduction:
You will fill a flask with water. You will heat the water and observe what happens to the volume of the water in the flask.
Observations:
When the liquid was heated, the level of liquid in the glass tube was seen to rise up the glass tube.
When the liquid was allowed to cool, the level of liquid was seen to drop.
Conclusion:
Liquids expand when heated and contract when cooled.

Question 6

What do liquids do when heated and cooled?

Answer 6

Liquids expand when heated and contract when cooled.

Question 7

What substance is an exception from expanding when heated and contracting when cooled? Explain this.

Answer 7

Water is an exception. As Water is cooled it too contracts. However, on reaching 4 degrees celsius, the water begins to expand again. Even after water has frozen and turned into ice, the ice expands too.
Every 100cm^3 of water turns to 109cm^3 of ice. The volume changes but the mass doesn’t change.

Question 8

At what temperature is the density of water the greatest?

Answer 8

The density of water is greatest at 4 degrees celsius.

Question 9

How do fish survive in lakes that are frozen?

Answer 9

The density of water is greatest at 4 degrees celsius. This means that water at any other temperature will float on it. (Density of water is 1, the density of ice is 0.9)

Question 10

Explain the introduction, observations and conclusions of an experiment that shows that gases expand when heat energy is added and that they contract when heat energy is lost.

Answer 10

Introduction:
You will heat gas in a flask and observe what happens to the volume of the gas as it is heated.
Observations:
As the gas (air) inside the flask is heated, bubbles of gas are seen to be coming out of the flask through the glass tube and into the water.
Conclusion:
Gases expand when they are heated. The volume of the gas became greater than the volume of the flask and the extra volume of air was pushed out of the flask.
Gases contract when cooled. The volume of the gas in the flask decreased and water was pulled into the flask to fill in space.

Question 11

Explain the movement of heat energy and give an example of this.

Answer 11

Heat energy moves naturally from a warm place to a colder place. A cold bottle of water will gain heat energy from its warmer surroundings until it reaches the same temperature as the surroundings.

Question 12

List the 3 main methods of heat transfer?

Answer 12

Convection, conduction and radiation

Question 13

Conduction definition

Answer 13

Conduction is the movement of heat energy through a substance without any overall movement of the substance itself.

Question 14

Show the transfer of heat energy by conduction and the different rates of conduction in different metals through an experiment.

Answer 14

Introduction:
You will heat different metals at one end and find out how long it takes the heat energy to pass through to the other side.
Observations & Conclusion:
The heat energy from the water has travelled along the metal rods to melt the vaseline.
Each substance conducts heat along its length. When the vaseline is heated above a certain temperature, it melts. The best conductor is the metal that conducts the heat fastest and causes the vaseline to melt first

Question 15

Give examples of conductors and insulators.

Answer 15

Insulator: Polystyrene, wool, fleece, foam
Conductors: (Metals), Mercury, gold, copper, brass

Question 16

definition of convection

Answer 16

Convection is the movement of heat energy through liquids and gases due to the motion of the substance itself.

Question 17

Why do particles of heated gas and liquid rise?

Answer 17

The particles move further apart, become less dense and rise.

Question 18

What are convection currents? Where do they not occur?

Answer 18

The upwards motion of warm particles and the downwards motion of cool particles is called a convection current. Convection does not happen in solids as the warmer particles cannot rise.

Question 19

Explain the experiment to show convection currents in a liquid

Answer 19

Introduction:
A crystal of dye is placed at the bottom of a beaker of water. The water is heated and the motion of the water can be observed.
Observation:
The water at the bottom of the beaker moves up. This motion of the water is shown by the movement of the dye in the water.
Conclusion:
As the water at the bottom of the beaker heats up, it rises. Cooler water sinks to take the place of the risen warmer liquid. This helps spread the heat all around the liquid. This movement of heat by the movement of the liquid is called convection.

Question 20

Explain the convection currents in a kettle.

Answer 20

When heating the liquid in a kettle, the heating element is placed at the bottom of the kettle. As the water around the heating element gets warm, it rises. This causes the entire contents of the kettle to be heated and not just the water around the heating element.

Question 21

Explain the experiment to show convection currents in air

Answer 21

Introduction:
A candle is used to heat the air. smoke is used to show how the air moves around the candle.
Observation and explanation:
The candle warms the air around it. This causes the air to rise in the chimney above it. Cold air is drawn towards the lighted candle and is sucked down into the chimney to replace the hot air that has risen.
Conclusion:
Hot air rises cold air falls.

Question 22

How do convection currents affect the weather?

Answer 22

The sun causes very large convection currents that we call winds.
The land warms up faster than the sea on hot days because hot air from the land rises. Cold air comes in from the sea to replace it. This causes an on-shore breeze.
At night the land cools faster than the sea. The air over the sea is warmer than the land and rises. Cooler air is pulled in from the land to replace the risen warmer air.

Question 23

radiation definition

Answer 23

Radiation is the transfer of heat energy via radiation waves that can travel through a vacuum.

Question 24

How does the energy from the sun get to the earth?

Answer 24

Radiation

Question 25

What do all warm objects emit? How can you see this?

Answer 25

All warm objects emit infrared light. You need to use a thermal camera or a night vision camera to see these as they are not visible to the naked eye.

Question 26

Explain the experiment that investigates heat transfer by radiation.

Answer 26

Introduction:
You will place an equal volume of hot water in 2 cans. One can is coloured white and the other black. Over a period of time, the temperatures of both cans are noted. The can that cools fastest is the best radiator.
Observations:
The temperature of the water in the black can decreases faster than water in the white or shiny can.
Conclusion:
Black dull materials radiate heat better than white shiny materials.

Question 27

How can radiation be reduced? Give examples of this.

Answer 27

Radiation can be reduced by using reflective surfaces like a mylar blanket which is used to keep a body warm.

Question 28

Latent heat definition

Answer 28

Latent heat is the energy needed to change the state of a substance without changing its temperature.

Question 29

Explain latent (hidden) heat using ice and an electric heater.

Answer 29

The ice is taken from the freezer at -16 degrees celsius and heated. The temp increases from -16 to 0. Then the energy is only used to melt the remaining ice. Since the energy is not causing an increase in temp, it is called latent heat as it is only changing its state.
When it is melted, the energy is used to change the temp until the water reaches 100. The energy will then stop increasing the temp of the water and begin changing its state from liquid to gas.

Question 30

Give examples of latent heat in everyday life

Answer 30

When you sweat, your body loses heat due to the water evaporating from the surface of your skin.
When steam is placed in cold milk, the steam changes state into a liquid and releases its latent heat to the milk, causing the milk to heat up quickly.
Ice cubes also absorb a lot of latent heat from a drink when they change state from solid to liquid.

Question 31

What do you use to measure joules? What is used to measure temperature?

Answer 31

A joule metre.

A thermometer.

Question 32

What is temperature the measure of?

Answer 32

Temperature the measure of how hot an object is