Unit 1: Chapter 1 - Energy Transfer By Heat

Question 1

What is Infrared Radiation?

Answer 1

Every object emits infrared radiation.

The hotter an object, is the more infrared radiation it will emit in agiven time.

Infrared is part of the electromagnetic spectrum. (Longer wavelength than visible light).

Infrared can penetrate the atmosphere but can’t leave the atmosphere. This is because objects emit longer wavelengths that can’t pass through the atmosphere.

Question 2

Surfaces and Radiation

-Best absorber or emitter?

Answer 2

The best absorbers are dark, matt surfaces of radiation.

On the other hand, shiny, smooth surfaces are better emitters of radiation.

Question 3

States of Matter

• Shape?
• Volume?
• Flow?
• Density?
• Change of state?
• kinetic theory of matter?

Answer 3

FLOW?

Solid - No
Liquid - Yes
Gas - Yes

SHAPE?

Solid - Fixed
Liquid - Fits container shape
Gas - Fills container

VOLUME?

Solid - Fixed
Liquid - Fixed
Gas - Can be changed

DENSITY?

Solid - Much higher than gas
Liquid - Much higher than gas
Gas - Low compared to solid and liquid

Change of State?
Gas -> Liquid - CONDENSATION
Gas -> Solid - CONDENSATION
Liquid -> Gas - VAPORISATION/BOILING
Liquid -> Solid - SOLIDFYING/FREEZING
Solid -> Gas - SUBLIMATION
Solid -> Liquid - MELTING

KINETIC THEORY OF MATTER?

Depends on the flow of the matter.

HIGH ENERGY: Gas
MEDIUM ENERGY: Liquid
LOW ENERGY: Solid

Question 4

Conduction

-How does it work?

Answer 4

Good conductors are good insulators.

Non-metals are worse conductors than metals because they don’t have free electrons.

How does it work?

• Ions vibrate clashing into other ions to transfer energy
• Free electrons, which orbit the ions get heated, gaining kinetic energy and diffuse out.
• Free electrons collide into ions, transferring kinetic energy. They also transfer energy to free electons.

Question 5

Convection

• How does it work?
• Where does convection take place?

Answer 5

Convection occurs within fluids only.

• Hot air rises next to heat source.
• Particles diffuse out and become less dense because the same mass of fluid occupies a larger volume which causes hot air to rise.
• Cold air sinks as it is more dense
• This produces a circulation current within the fluids

Convection currents occur near coasts but also within the Earths mantle.

Question 6

Evaporation

How exactly does it work?

How might it be useful?

What are the factors that affect evaporation?

Answer 6

Evaporation is the process of a liquid changing to gas.

There are weak attractive forces existing between molecules in a liquid.

The molecules with the most kinetic energy break away from attraction of other molecules.

The liquid itself is cooler because the average kinetic energy of remaining molecules decrease.

THE USE OF ALCOHOL BEFORE INJECTION

An example of evaporation is the use of alcohol that easily evaporates before injecting a needle. As the liquid evaporates, your skin becomes too cold to feel any pain.

FACTORS THAT AFFECT EVAPORATION

• Larger surface area in contact with dry air.
• Any heat source on the liquid. Warmer they are, the faster it evaporates.
• Any draught of air to take away molecules of water across the liquid surface.

Question 7

Condensation

How exactly does it work?

What factors affect condesation?

Answer 7

Condensation is the change of gas into liquid or solid.

Water molecules collide into the surface (mirror) and some stay there. This is condensation.

FACTORS AFFECTING THE RATE OF CONDENSATION

• Increase of surface area
• Reducing the temperature of the surface

Question 8

Energy transfer by design

Answer 8

Rate of energy depends on:

• The materials the object is in contact with
• The material of the object
• The object’s shape
• The objects surface area
• The temperature difference between the object and the surroundings

Question 9

Specific Heat Capacity

How do you calculate Specific Heat Capacity?

What does this mean?

Where might specific heat capacity take place in daily activities?

Answer 9

HOW DO YOU CALCULATE SPECIFIC HEAT CAPACITY?

Temperature rise of an object depends on:

• AMOUNT of ENERGY supplied to it
• MASS of the substance
• WHAT the SUBSTANCE IS

Specific heat capacitys units are J/KgC

Ø = temperature change (C) (Final temp - Start temp)

E = energy supplied in joules (J)

m = mass of object (Kg)

c = Specific Heat Capacity

NOTE: Mass must be in Kg.

c = E/(m x ø)

WHAT DOES THIS MEAN?

This means that the higher the specific heat capacity, the more energy it will retain.

WHERE MIGHT SPECIFIC HEAT CAPACITY TAKE PLACE IN DAILY LIFE?

An example would be storage heaters at off-peak times. The storage heater has a high specific heat capacity. Off-peak times sometimes charge cheaper prices, so storage heaters are designed to be cost-effective.

Question 10

Heating and Insulating Buildings

What are the ways to save money by reducing energy transfer rate at home?

What are U-Values?

How does the Solar Heating Panels work?

Answer 10

LOFT INSULATION - fibre-glass is used as an insulator. Air between fibres reduce energy transfer through CONDUCTION.

CAVITY WALL INSULATION - Cavity is pumped between walls to REDUCE CONVECTION CURRENTS by trapping air in small air pockets.

ALUMINIUM FOIL behind radiator -REFLECTS RADIATION as aluminium is shiny.

DOUBLE-GLAZED WINDOWS - Dry air or a vacuum between panes and reduced energy transfer by CONDUCTION. A vacuum cuts energy transfer rate through CONVECTION.

U-VALUES

Calculates the J/s that passes through 1 metre squared of material when the temperature difference across is 1C.

LOWER THE U-VALUE, MORE EFFECTIVE MATERIAL AS AN INSULATOR.

SOLAR HEATING PANELS

The copper pipes are on a MATT BLACK metal plate and the pipes are connected to the heat exchangers in the water storage tank.

A transparent cover on top of the panel allows radiation to pass through easier. Insulating under the panel stops energy passing through the back panel.