Effects of Heat and its Transmission

Question 1

What happens to a substance when it’s heated?

Answer 1

It expands and increase in volume as its particles move further apart.

Question 2

What happens when a substance is cooled?

Answer 2

It contracts and decrease in volume as its particles move closer together.

Question 3

State the matter that expands and contracts the least and most. starting from the least.

Answer 3

Solid, liquid, gas.

Question 4

What is the quantity symbol, SI unit and SI unit symbol for temperature?

Answer 4

T, kelvin, K

Question 5

Why do MRT tracks have gaps?

Answer 5

It is to allow the tracks to expand on hot days. This is to prevent the tracks from warping/distorting.

Question 6

What feature do water pipes have to prevent damage on hot days?

Answer 6

Water pipes have bends to allow expansion on hot days.

Question 7

Why are overhead cables hung loosely?

Answer 7

It is to allow contraction during cold weathers. This is to prevent the cables from snapping.

Question 8

What are 2 features of bridges to prevent damage during hot days?

Answer 8

• Expansion gaps to provide space for the bridge to expand on hot days.
• Rollers at one end of the bridge to allow the bridge to expand easily.

Question 9

When heated, which material, iron or brass, expands more and is outside of the curve?

Answer 9

Brass.

Question 10

When cooled, which material, iron or brass, contracts least and is outside the curve?

Answer 10

Iron.

Question 11

How are bimetallic strips used in thermostats?

Answer 11

When the switch contacts are touching each other, current flows in the circuit, causing the bimetallic strip to heat up. Brass expands more than iron, thus when the temperature is too high, the bimetallic strip bends away from the switch contacts. This stops the current from flowing in the circuit, causing the temperature to drop.

Question 12

State the change in setup if the thermostat is to be connected to a cooler circuit in a refrigerator.

Answer 12

The brass is on the inside of the curve and the iron is on the outside of the curve.

Question 13

Is a medium present in conduction?

Answer 13

Yes.

Question 14

Is a medium present in convection?

Answer 14

Yes.

Question 15

Is a medium present in radiation?

Answer 15

No.

Question 16

Which state of matter can conduction occur in?

Answer 16

In solids (mainly), liquids and gases.

Question 17

Which state of matter can convection occur in?

Answer 17

Only in liquids and gases.

Question 18

Which state of matter can radiation occur in?

Answer 18

In vacuum, gases (mainly), liquids and solids.

Question 19

Is there movement needed in the medium during conduction?

Answer 19

No.

Question 20

Is there movement needed in the medium during convection?

Answer 20

Yes.

Question 21

Is there movement needed in the medium during radiation?

Answer 21

No.

Question 22

What is the direction of heat flow in conduction?

Answer 22

All directions.

Question 23

What is the direction of heat flow in convection?

Answer 23

Upwards.

Question 24

What is the direction of heat flow in radiation?

Answer 24

All directions.

Question 25

How does transfer of heat in conduction happen?

Answer 25

It only occurs when there is a temperature difference, from a region of higher temperature to a region of lower temperature.

Question 26

When is there no net flow of heat between two bodies in conduction?

Answer 26

When two bodies are in thermal equilibrium.

Question 27

Why is a kettle that is used to boil water made of metal?

Answer 27

Metal is a good conductor of heat. Heat travels by conduction from the fire to the water quickly, hence, allows the water to boil quickly.

Question 28

Why is an ice cream container made of plastic?

Answer 28

Plastic is a poor conductor of heat. Heat travels by conduction from the surroundings to the ice cream slowly, hence, the ice cream will not melt so quickly.

Question 29

What is the definition of convection?

Answer 29

The transfer of heat from one place to another by the movement of fluids.

Question 30

What are the changes in fluids that are heated?

Answer 30

The temperature of it increases, the particles expand and increase in volume, becomes less dense and rises.

Question 31

What are the changes in fluids that are cooled?

Answer 31

The temperature of it decreases, the particles contract and decrease in volume, becomes denser and sinks

Question 32

How does convection happen when a liquid is heated at the bottom?

Answer 32

The bottom of the liquid gets heated, expands, becomes less dense and rises. The surrounding cooler and denser liquid sinks to replace the rising hot water to be heated again. This process of rising and sinking repeats, forming convection currents.

Question 33

How does convection take place when a liquid is cooled at the top?

Answer 33

The top of the liquid gets cooled, contracts, becomes denser and sinks. The surrounding hotter and less dense liquid rises to replace the sinking cooler liquid to be cooled again. This process of sinking and rising repeats, forming convection currents.

Question 34

Why do kettles have lids?

Answer 34

This is to prevent the air above the hot water from rising and hence prevents transfer of heat from the hot water to the surroundings by convection currents.

Question 35

Is white or black a good emitter of infra-red radiation?

Answer 35

Black.

Question 36

Is a smooth texture a poor emitter?

Answer 36

Yes.

Question 37

Is a large or small surface area better for emitting infra-red radiation?

Answer 37

Large surface area.

Question 38

Is white or black a poorer absorber of infra-red radiation?

Answer 38

White.

Question 39

Is a rough texture a poorer absorber of infra-red radiation?

Answer 39

No.

Question 40

Is a large or small surface area worse for absorbing infra-red radiation?

Answer 40

Small surface area.

Question 41

Is a black or white board a better absorber of infra-red radiation? Explain.

Answer 41

Black board is a better absorber of infra-red radiation than white board. Heat will travel by radiation from the sun to the black board faster than to the white board, hence, the black board will heat up quicker.

Question 42

Is a rough or smooth surface beaker better at emitting infra-red radiation?

Answer 42

The rough beaker is a better emitter of infra-red radiation than a smooth beaker. Heat will travel by radiation from the hot water in the rough beaker to its surroundings faster than from the smooth beaker, hence, the water in the rough beaker will loose heat more quickly than in the smooth beaker.