Chapter - 11 (Thermal Energy Transfer)

Question 1

What are Good thermal conductors?

Answer 1

Solids (Ex - metal pan or ceramic cup)

Tiles
Stones

Question 2

What are bad thermal conductors (insulators)?

Answer 2

• Wollen blanket
• Layers of paper & carpet

Question 3

Why do we feel the tile is cold?

Answer 3

• Heat is transferred away from the foot making the tile feel colder

Question 4

why do we not feel cold on the rug?

Answer 4

• Insulators
• Heat is not transferred away from the foot

Question 5

Which state does conduction happen in?

Answer 5

solids

Question 6

When does conduction occur?

Answer 6

Two solids of different temperatures come in contact with one another, thermal energy is transferred from the hotter objects to the cooler objects.

Question 7

Why are metals the best conductors?

Answer 7

They have free electrons

Question 8

What are the 2 mechanisms that conduction happens in?

Answer 8

• Atomic vibrations
• Free electrons collisions

Question 9

What happens when a substance is heated?

Answer 9

• Ions move around and vibrate
• they bump into each other
• collision transfer thermal energy until thermal equilibrium is reached

Question 10

Why does conduction not happen easily in fluids?

Answer 10

• Particles are close together but slide past each other
• gas particles are too far apart

Question 11

In which states does convection happen in?

Answer 11

Liquids and gases

Question 12

What happens when liquid or gas is heated?

Answer 12

• Molecules push each other apart making the liquid or has expand.
• hot liquids n gas becomes less dense
• hot liquid/gas rises
• hot liquid/gas eventually cools down and sinks again.
• the convection current then repeats

Question 13

What happens when a liquid or gas is cooled?

Answer 13

• molecules move together making the liquid/gas contract.
• This makes hot liquid/gas more dense than surroundings

Question 14

How can you demonstrate convection currents?

Answer 14

Take a beaker and add potassium permanganate

Question 15

How does the hotness affect the thermal radiation?

Answer 15

The hotter the object is, more thermal radiation it emits.

Question 16

What is thermal radiation a part of?

Answer 16

Electromagnetic spectrum called infrared

Question 17

What is thermal radiation a way?

Answer 17

The only way in which heat can travel in vacuum

Question 18

What happens when an object absorbs thermal energy?

Answer 18

• It emits more thermal radiation

Question 19

What happens when the temp of the body increases?

Answer 19

Absorbs radiation faster than it emits radiation

Question 20

What happens when an object is absorbing at the same rate it is emitting radiation?

Answer 20

• Constant temp
• Thermal equilibrium

Question 21

When will the object cool down?

Answer 21

If the rate at which an object receives energy is less than the rate at which it transfers energy away.

Question 22

When will the object heat up?

Answer 22

If the rate at which an object transfers energy is away is less than the rate at which it receives energy

• always moves to thermal equilibrium

Question 23

What are the factors that’s effect the thermal radiation emitted?

Answer 23

• Surface colour (Black = more radiation)
• Texture (Shiny surfaces = more radiation)
• surface area (greater surface area = more area for radiation)

Question 24

What would happen if the Earth had no atmopshere?

Answer 24

Temp on the earth’s surface will drop to - 180°C at night (same as moon’s temp surface)

Question 25

Why does the temp of the surface on earth drop in absence of Earth’s atmosphere?

Answer 25

The surface might emit all radiation from sun into space.

Question 26

What factors is the temp on earth affect by?

Answer 26

Balance between incoming radiation and radiation emitted

Question 27

How does the earth emit thermal radiation?

Answer 27

With a slightly longer wavelength than the thermal radiation it receives.

Question 28

How do gases on Earth absorb and emit thermal radiation?

Answer 28

Water vapour, methane, and CO 2 absorb and reflect back longer - wavelength infrared radiation and prevent it from escaping into space.

Question 29

What do the gases in atmosphere do in simpler terms?

Answer 29

Absorb radiation and emit back to the surface

Question 30

What factors do the earth’s temp depend on?

Answer 30

Rate at which light and infrared radiation from the sun are:

• Reflected back into space
• Absorbed by the atmosphere or by earth’s surfaces
• emitted from the earth’s surface and from earth’s surface

Question 31

What contributes to the greenhouse effect?

Answer 31

Rate of absorption and emission of radiation on earth

Question 32

What happens when the sun’s thermal radiation reaches the earth’s atmosphere?

Answer 32

• Some radiation is reflected back to space
• any radiation not reflected is absorbed and re-radiated by greenhouse gases

Question 33

In which state