P2 - Energy Transfer by Heating

Question 1

What is a Conductor?

Answer 1

A conductor allows the flow of charge.

Question 2

What type of material is the best conductor of energy?

Answer 2

Metals

Question 3

Why are metals such good conductors?

Answer 3

Their bonding enables a ‘sea’ of delocalised electrons to carry charge through the metal.

Question 4

What is an insulator?

Answer 4

An insulator resists the flow of charge.

Question 5

How are insulators bonded?

Answer 5

Their electrons are held much more tightly together and will resist the flow of charge (no electrons can move through them).

Question 6

What makes a good insulator?

Answer 6

• Thick

- Low thermal conductivity

Question 7

What is Conduction?

Answer 7

The process by which heat energy is transferred by collisions with neighbouring molecules.

• Conduction occurs mostly in solids.
• BUT CAN ALSO HAPPEN IN SOME LIQUIDS AND GASES.

Question 8

What are some examples of Conduction?

Answer 8

1) Melting chocolate - heat transferred from the hand to the chocolate.
2) Ironing a shirt - heat transferred from the iron to the shirt.

Question 9

What is thermal conductivity a measure of?

Answer 9

A measure of how well a material can conduct heat.

Question 10

What does having a higher thermal conductivity mean?

Answer 10

It means more energy can be transferred (better conductor).

Question 11

Which is a better conductor - copper or steel?

Answer 11

Copper - whence why it’s used in wires

Question 12

How does thickness impact conductivity?

Answer 12

The thicker a material, the slower it will allow the flow of charge.

Thin = Good conductor

Question 13

What is Convection?

Answer 13

The movement within a fluid caused by hotter (less dense) material to rise, and colder (more dense) material to sink under the influence of gravity.

Question 14

What state does convection take place?

Answer 14

All fluids - liquids and gases.

Question 15

How does convection work?

Answer 15

1) Fluid heated up.
2) Hotter, less dense material rises.
3) Cooler, more dense material sinks, replacing the hot material.
4) A ‘convection current’ is set up.

Question 16

What does ABSORB mean?

Answer 16

To take in.

Question 17

What does REFLECT mean?

Answer 17

To bounce back or mirror.

Question 18

What does RADIATE mean?

Answer 18

To give out waves or rays.

Question 19

What does TRANSMIT mean?

Answer 19

To let waves or rays through.

Question 20

What does EMIT mean?

Answer 20

To give off.

Question 21

What is black like as an absorber and emitter of heat?

Answer 21

Black is an excellent absorber and emitter of heat - the best.

Question 22

Why is black a good absorber and emitter of heat?

Answer 22

Black absorbs all incoming light.

Question 23

What is white like as an aborber and emitter of heat?

Answer 23

White is a poor absorber and emitter of heat - the worst.

Question 24

Why is white a poor absorber and emitter of heat?

Answer 24

White reflects all incoming light.

Question 25

Why can people with darker skin cool themselves down more effectively?

Answer 25

Darker skin absorbs more heat - but this does not increase the body's internal heat temperature. Darker skin can emit the heat absorbed by the skin and from the body.

Question 26

How do shiny surfaces and matt surfaces compare in terms of absorption and emission?

Answer 26

Matt surfaces are the best absorbers and emitters. Shiny surfaces are the worst absorbers and emitters.

Question 27

What is radiation?

Answer 27

Radiation is waves of energy.

Question 28

What is infrared radiation?

Answer 28

A type of electromagnetic radiation which we feel as heat.

Question 29

How do infrared rays/waves differ from light rays in terms of wavelength?

Answer 29

Infrared radiation is before visible light on the EM spectrum - so infrared rays have longer wavelengths.

Question 30

What speed do infrared rays travel at?

Answer 30

300,000,000 m/s - speed of light

Question 31

Why are infrared cameras used for security and in the police?

Answer 31

All objects emit and absorb infrared radiation. Things that respire (i.e people) are heat sources and can easily be identified.

Question 32

How does the temperature of something impact the infrared radiation it emits?

Answer 32

The hotter an object, the more infrared it emits.

Question 33

How does the sun transfer heat energy to the earth?

Answer 33

The Sun heats the earth by infrared radiation which travels through the vaccum of space. As space is a vaccum - no heat transfer can take place by conduction or convection.

Question 34

What is a perfect black body?

Answer 34

An object that absorbs and then re-emits ALL of the radiation that hits it. -NO reflection or transmission (nothing passes through it).

Question 35

What is blackbody radiation?

Answer 35

The radiation emitted by a body that absorbs all radiation that hits it.

Question 36

How does the intensity of blackbody radiation vary with wavelength?

Answer 36

Shorter wavelength = Greater heat intensity | Hotter object = shorter wavelength

Question 37

What does the temperature of the earth's surface depend on?

Answer 37

The balance between the absorbtion and emission of infrared radiation. Absorption > Emssion —> °C Increases Absorption < Emission —> °C Decreases

Question 38

How can a system stay at a constant temperature - theoretically?

Answer 38

A system will remain at a constant temperature if: Absorption = Emission

Question 39

How are emergency/space blankets used to keep someone warm?

Answer 39

By keeping the heat that is generated by the body from emitting into the surrounding air.

Question 40

How do barns use infrared lamps to keep the animals warm?

Answer 40

You can't have fire as there is a lot of wood and hay. Therefore infrared lamps give out heat to the barn.

Question 41

What is Specific Heat Capacity?

Answer 41

The amount of thermal energy needed to raise the temperature of 1kg of a substance by 1°C or 1K. Units: J/kg High Specific heat capacity = more energy needed. Low Specific heat capacity = less energy needed.

Question 42

What is the equation used to calculate energy that involves specific heat capacity?

Answer 42

Energy Transferred = mass x specific heat capacity x temperature change E = m x c x Δt (J) = (kg) x (J/kg) x (°C or K)

Question 43

By re-arranging this equation, how do you calculate specific heat capacity?

Answer 43

c = E / m x Δt

Question 44

What is the Specific Heat Capacity Required Practical?

Answer 44

Aim: To calculate the specific heat capacity of aluminium, using a circuit. 1) Measure the current, voltage and temperature of the materials at certain intervals. 2) Use E = IVt (Energy = Current x Voltage x time) to work out E. 3) Then do c = E / m x Δt (temperature)

Question 45

How are homes heated?

Answer 45

Gas or oil-fired central heating.

Question 46

How can the rate of energy transfer out of a home be reduced? (Saves money and warms house)

Answer 46

1) Loft Insulation - Loft insulation reduces the rate of energy transfer through the roof. Fibreglass is used. 2) Cavity Wall Insulation - The Cavity of an outer wall is the space between the 2 layers of brick that make up the wall. The insulation is pumped into the cavity and reduces the rate of energy transfer by conduction. 3) Double Glazed Windows - Double glazed windows have two glass panes with dry air or a vacuum between the panes. The dry air reduces the rate of energy transfer by conduction and a vacuum prevents convection. 4) Alluminium Foil behind radiators - The foil reflects radiation away from the wall and reduces energy transfer by radiation.