Chapter 10: Heat

Question 1

Define ‘temperature’

Answer 1

It is a measure of how hot an object is

Question 2

What is the SI unit for temperature?

Answer 2

Kelvin (K)

Question 3

What happens when 2 objects are in contact? (Heat transfer)

Answer 3

Heat energy is transferred from the hotter object to the colder object. This causes the temperature of the hotter object to decrease and the temperature of the colder object to increase until both objects reach the same temperature/ equilibrim.

Question 4

What happens to a substance upon heating?

Answer 4

It will gain heat and expand, causing its volume to increase while its density decreases.

Question 5

What happens to water upon heating from the heat source below a pot of water?

Answer 5

The water at the bottom will gain heat and expand, causing its volume to increase and its density to decrease. This causes the water to rise to the top, thus forming a convection current

Question 6

What happens when water at 0-4°C is heated? (Short ans)

Answer 6

It will gain heat and contract. (vice versa)

Question 7

What happens to a solid upon cooling?

Answer 7

The solid will lose heat and contract, causing the volume to decrease and its density to increase.

Question 8

Which state of matter does expansion occur the most and least in?

Answer 8

Most: Gas
Least: Solid

Question 9

What happens when a liquid is cooled?

Answer 9

It will lose heat and contract, causing its volume to decrease and its density to increase, thus cool water sinks, which creates a convection.

Question 10

What state of matter does contraction occur the most and the least in?

Answer 10

Most: Gas
Least: Solid

Question 11

What are some examples of real-life applications to counter effects of expansion and contraction?

Answer 11

1. Gaps between railway tracks
2. Sagging telephone lines
3. Rollers on bridge

Question 12

What are bimetallic strips used in?

Answer 12

Thermostats.

Question 13

What does a thermostat do?

Answer 13

It helps to keep the temperature of an appliance constant.

Question 14

What is a bimetallic strip?

Answer 14

It is made out of two different metals welded together where one expands and contracts more than the other upon the same change in temperature.

Question 15

If the brass is on the bottom of bimetallic strip, what happens when it is heated up?

Answer 15

Brass will expand more and become longer, causing the bimetallic strip to bend upwards.

Question 16

If brass was on the bottom of the bimetallic strip and it expands and contracts more than the other metal, what would happen when it is cooled?

Answer 16

Brass will contract more and it will become shorter, causing the bimetallic strip to bend downwards.

Question 17

What is conduction?

Answer 17

It is the transfer of heat energy without the physical movement of the medium.

Question 18

How is heat transferred via conduction?

Answer 18

The heat source will heat up the object. The hotter end of the object has a high vibration of atoms, meaning that the particles will become faster as there is more heat energy. Particles in the object collide with each other and pass on the heat energy to the next particles until the object reaches an equilibrim

Question 19

Why does conduction take place the best in solids?

Answer 19

The particles are the closest to each other and can transfer the heat energy from one particle to another particle the quickest.

Question 20

Why can’t conduction occur in vacuum?

Answer 20

There are no particles at all.

Question 21

Why does conduction occur the best in metals?

Answer 21

There are free moving electrons to help transfer the heat energy from one end of the material to the other end.

Question 22

What is the factor that affects the rate of conduction?

Answer 22

Different materials

Question 23

What is convection?

Answer 23

It is the transfer of heat energy from one place to another by the physical movement of a medium.

Question 24

What states of matter can convection take place in?

Answer 24

Liquid and gas.

Question 25

What causes a convection current to be set up?

Answer 25

Because of the changes in density

Question 26

What are the conditions needed for a convection current to be set up effectively?

Answer 26

Heat source must be at the bottom OR cooling source must be at the top

Question 27

What is radiation?

Answer 27

The transfer of energy from a hotter body to a cooler body without the need for a medium.

Question 28

What are the 3 factors that affect rate of radiation?

Answer 28

1. Temperature of object
2. Surface area of object
3. Type of surface (Texture and colour)

Question 29

What is the relationship between radiation and the temperature of an object?

Answer 29

The hotter the body of an object, the higher the rate of radiation from the object.

Question 30

Why do objects with a larger surface area have a higher rate of radiation?

Answer 30

The large surface area allows heat to be radiated away quickly.

Question 31

What are the characteristics of black/ dark and dull and rough surfaces?

Answer 31

They are better emitters and absorbers of radiation.

Question 32

What are the characteristics of white/ light and smooth and shiny surfaces?

Answer 32

They are poor emitters and absorbers of radiation.