P1.1 Energy Transfer By Heating

Question 1

Define infrared radiation.

Answer 1

A type of electromagnetic radiation which involves waves rather than particles. It can pass through a vacuum.
All objects emit IR and the hotter the object the more IR it emits.

Question 2

What surface is the best emitter and best absorber?

Answer 2

Matt black

Question 3

What surface is the worst emitter and worst absorber?

Answer 3

Shiny silver

Question 4

Why are solar heating panels painted black?

Answer 4

The panels have to absorb heat radiation as quickly as possible. Black is the best absorber of IR

Question 5

Describe how particles are structured in a solid.

Answer 5

The particles are in a structured position and are very dense and won’t flow. The particles vibrate but stay in a fixed position.

Question 6

Describe how particles are structured in a liquid.

Answer 6

The particles aren’t fixed and are in a random position. They flow easily and have a lower density than a solid but a higher density than a gas.

Question 7

Describe how particles are structured in a gas.

Answer 7

The particles are completely random and free to flow anywhere. The density in very low. You can’t see the particles flowing but they’re quite fast. They are not in a fixed position.

Question 8

How does conduction happen in non metals?

Answer 8

The particles are heated and they vibrate and collide with neighbouring particles. The heat energy is then slowly passed on.

Question 9

Why are metals good conductors?

Answer 9

Free electrons

These can move throughout the solid and collide with more particles.

Question 10

What’s a fluid? How is heat energy transferred in a fluid?

Answer 10

A fluid is a liquid or gas.
The heated fluid particles gain energy so they move about more and spread out. The same number of particles now take up more space so the fluid has become less dense.

Question 11

Why is a liquid cooler after evaporation?

Answer 11

Weak attractive forces exist between the molecules in the liquid. The faster molecules, which have more kinetic energy, break away from the attraction of the other molecules and escape from the liquid. After they leave, the liquid is cooler because the average kinetic energy of the remaining molecules in the liquid has decreased.

Question 12

The rate at which an object transfers energy by heating depends on……..

Answer 12

Surface area
Volume
Material
Temperature difference

Question 13

How does a vacuum flask limit heat transfer?

Answer 13

Silvered surfaces reflect heat back into the liquid
The vacuum limits evaporation, convection and conduction
The plastic cork stops evaporation and convection
Metal casing is a good conductor so heat outside can transfer in

Question 14

What’s in double glazed windows that limit heat transfer?

Answer 14

Vacuum between the two panes

Question 15

How does loft insulation stop heat transfer?

Answer 15

Stops the heat energy rising out of the house. Insulation limits convection and conduction.

Question 16

How do draught excluder doors stop heat transfer?

Answer 16

Stops convection

Warm air is trapped in the house

Question 17

How does carpet stop heat transfer?

Answer 17

Stops conduction

Cold heat energy can’t be transferred from underneath to the house

Question 18

How does cavity wall insulation stop heat transfer?

Answer 18

Stops conduction and convection.

Between the bricks and wall there might be a vacuum. Heat energy is trapped in the room. The wall isn’t a good conductor

Question 19

How do curtains stop heat transfer?

Answer 19

Stops convection

The air between the window and curtain is trapped. Stops heat energy passing out through windows

Question 20

How do radiator reflectors stop heat transfer?

Answer 20

Stops radiation. Reflects the heat energy back into the radiator and then back to your room

Question 21

What’s a U-value?

Answer 21

The measure of heat energy transfer.
The more heat energy transferred, the higher the U-value.
The lower the U-value, the better the material is as an insulator.

Question 22

What measures the insulation on a duvet?

Answer 22

Tog rating

The higher the rating the more insulating

Question 23

How do you calculate specific heat capacity?

Answer 23

Energy / (mass X temperature difference)

Question 24

What is specific heat capacity?

Answer 24

The energy needed to raise the temperature of a 1 kg mass by 1 degrees c

Question 25

What’s the unit of specific heat capacity?

Answer 25

J/kg degrees c

Question 26

What’s payback time?

Answer 26

The time it takes for the cost of installing insulation to be equalled by the savings made from reduced energy costs.

Question 27

How do you calculate payback time?

Answer 27

Cost of insulation / saving each year

Question 28

Silver reflectors cost £25 and saves £50 per year. What’s the payback time?

Answer 28

25/50

0.5 years or 6 months

Question 29

Why do people still install double glazed windows even if the payback time is soooo long?

Answer 29

Because it looks nicer and is safer.