Energy Transfer by Heating

Question 1

Give four facts about infrared radiation.

Answer 1

1) Infrared waves are part of the electromagnetic spectrum.
2) ALL objects emit infrared radiation
3) The hotter an object is the more infrared radiation it emits in a given time.
4) Infrared radiation can travel through a vacuum, as in travelling through space (this is how we get energy from the sun)

Question 2

What colour surfaces are the best absorbers?

Answer 2

Dark, matt surfaces

Question 3

What colour surfaces are the best emitters?

Explain how this affects objects that are painted this colour.

Answer 3

Dark, matt surfaces
An object that is painted dull black will transfer energy and cool down more quickly than the same object painted shiny white.

Question 4

What colour surfaces are best at reflecting infrared radiation?

Answer 4

Light, shiny surfaces

Question 5

Describe the structure and characteristics of a solid.

Answer 5

Particles in a solid are held together in a rigid 3D structure, the particles vibrate about fixed positions.
Solids have a fixed shape and volume.

Question 6

Describe the structure and characteristics of a liquid.

Answer 6

The particles in a liquid are in contact with each other but can move about at random.
Liquids do not have a fixed shape and can flow which means they will fill the container in which they are placed.

Question 7

Describe the structure and characteristics of a gas.

Answer 7

The particles in a gas are usually much further apart and move about at random, much faster.
A gas doesn’t have a fixed shape and can flow and the density of a gas is much less than that of a solid or liquid.

Question 8

Explain the process of conduction in a non-metal.

Answer 8

If one end of a solid is heated, the particles at that end gain kinetic energy and vibrate more, this energy is transferred to neighbouring particles and in this way the energy is transferred through the solid.

Question 9

Explain an alternative method of conduction that occurs in metals only.

Answer 9

Metals contain free electrons, when the metal is heated these free electrons gain kinetic energy and move through the metal. As they do so they transfer energy by colliding with other particles.
Hence all metals are good conductors.

Question 10

What is another name given to poor conductors?

Give examples of materials that are good … and explain why they are good …

Answer 10

Insulators

Materials such as wool and fibreglass are good insulators because they contain trapped air.

Question 11

Explain the process of convection?

Answer 11

Convection occurs in fluids (liquids and gases) only.
When a fluid is heated it expands, the fluid becomes less dense and rises. The warm fluid is replaced by cooler denser fluid. As the fluid rises it cools down and becomes more dense so it begins to fall and return to its original position.
The resulting convection current transfers energy throughout the fluid.

Question 12

Give one example of convection on a small scale and convection on a large scale.

Answer 12

Small scale - heating water in a beaker

Large scale - heating the air above land and sea, convection current are responsible for onshore and offshore breezes.

Question 13

Explain the process of evaporation and explain why the temperature of the liquid decreases when evaporation occurs.

Answer 13

Evaporation is when a liquid turns into a gas, evaporation takes place because the most energetic liquid molecules escape from the surface of the liquid and enter the air.
As a result the average kinetic energy of the remaining molecules is less, so the temperature of the liquid decreases.

Evaporation causes cooling

Question 14

Give three factors that increase the rate of evaporation.

Answer 14

1) Increasing the surface area of the liquid
2) Increasing the temperature of the liquid
3) Creating a draught across the surface of the liquid.

Question 15

Explain the process of condensation and state where it usually takes place.

Answer 15

Condensation is when a gas turns into a liquid, this often takes place on cold surfaces such as windows and mirrors.

Question 16

Give two factors which increase the rate of condensation.

Answer 16

1) Increasing the surface area

2) Reducing the surface temperature

Question 17

Give four factors that affect the rate at which energy is transferred.

Answer 17

1) The temperature difference between an object and its surroundings
2) The materials an object is in contact with
3) The object’s shape
4) The object’s surface area

Question 18

To maximise the rate of energy transfer to keep things cool what kind of objects do we use? (3)

Answer 18

1) Object’s made of materials that are good conductors
2) Object’s painted dull,black
3) Object’s that have the air flow around them maximised.

Question 19

To minimise the rate of energy transfer to keep things warm what kind of objects do we use?

Answer 19

The transfer of energy by conduction, convection and radiation should be minimised. We should use things that:

1) Are good insulators
2) Are white and shiny
3) Prevent convection currents by trapping air in small pockets.

Question 20

What is the specific heat capacity of a substance?

Answer 20

The specific heat capacity of a substance is the amount of energy required in joules to raise the temperature of 1 kilogram of the substance by 1 degree celsius.

Question 21

What is the equation for specific heat capacity?

Answer 21

E = m x c x theta
E is energy transferred in joules, J
m is the mass, kg
c is specific heat capacity, J/kgºC
theta is temperature change, ºC

Question 22

What is a U-value and what does a low U-value indicate?

Answer 22

The U-value of a material tells us how much energy per second passes through it, the lower the U-value the better the material is as an insulator.

Question 23

What is a solar heating panel and what is it used for?

Give one advantage and one disadvantage of a solar heating panel.

Answer 23

A solar heating contains water that is heated by radiation from the sun, this water may be used to heat buildings or as a domestic hot water supply.
Advantage:
Solar heating panels are cheap to run because they do not use fuel.
Disadvantage:
They are expensive to buy and install and the water is not heated at night.