P1.1 - Energy transfer by heating

Question 1

How does the temperature of an object affect the rate at which it emits infrared radiation?

Answer 1

The hotter the object, the more infrared radiation it gives off.

Question 2

What is a vacuum?

Answer 2

A space with no particles.

Question 3

In terms of IR, what are dark, matt surfaces?

Answer 3

Good absorbers, good emitters and poor reflectors of IR.

Question 4

In terms of IR, what are light, shiny surfaces?

Answer 4

Poor absorbers, poor emitters and good reflectors of IR.

Question 5

What are the three states of matter?

Answer 5

The three states are:
Solid
Liquid
Gas

Question 6

Describe the organisation of particles in a solid.

Answer 6

Particles are held next to each other.

They vibrate in their fixed positions.

Question 7

Describe the organisation of particles in a liquid.

Answer 7

Particles move about at random.

They are in contact with each other.

Question 8

Describe the organisation of particles in a gas.

Answer 8

Particles move about at random.
They move much faster [than a solid or a liquid].
They are much farther apart [than a solid or a liquid].
They have a lower density [than a solid or a liquid].

Question 9

What is conduction?

Answer 9

Transfer of energy from particle to particle, in matter.

Question 10

What are good conductors?

Answer 10

Metals and solids.

Question 11

What are poor conductors?

Answer 11

Most liquids and gases.

Question 12

What is an insulator, and give an example.

Answer 12

A poor conductor (bad at transferring energy)

Examples are: wool and fiberglass.

Question 13

Why does conduction happen in a metal?

Answer 13

They have free electrons which gain kinetic energy.
These move through the metal.
They transfer energy by colliding with other particles.

Question 14

How does conduction happen?

Answer 14

At the end heated, the particles gain kinetic energy.
This causes them to vibrate more.
This energy in transferred to neighboring particles.
The process carries on up the object.

Question 15

Why are non-metals poor conductors (insulators)?

Answer 15

They contain trapped air.

They don’t contain any free electrons.

Question 16

What is convection?

Answer 16

The circulation of a fluid (ONLY IN liquid or gas) caused by heating it.

Question 17

What is a convection current?

Answer 17

The circular motion of matter caused by heating fluids.

Question 18

In terms of density, how does convection happen?

Answer 18

Heating a liquid or gas makes it less dense.
This causes it to rise.
Warm fluid is replaced by denser fluid.
This causes a circulation.

Question 19

What is evaporation?

Answer 19

It is when a liquid turns into a gas.

Question 20

What causes evaporation to occur, and what happens to the liquid the particle has evaporated from?

Answer 20

• The most energetic liquid molecules escape from the liquid’s surface and enter the air.
• The average kinetic energy of remaining molecules is less; temperature of liquid decreases.
• Evaporation causes cooling.

Question 21

Name 3 things the rate of evaporation is increased by.

Answer 21

• Increasing the surface area of a liquid.
• Increasing the temperature of a liquid
• Creating a draught of air across the liquid’s surface.

Question 22

What is condensation?

Answer 22

It is when a gas turns into a liquid.

Question 23

Name 2 things the rate of condensation is increased by.

Answer 23

• Increasing the surface area.

- Reducing the surface temperature.

Question 24

Name the relationship between temperature difference and the rate of energy transfer.

Answer 24

The greater the temperature difference between an object and its surroundings, the greater the rate at which energy is transferred.

Question 25

What does the rate at which energy is transferred depend on (3 things)?

Answer 25

• The materials the object is in contact with
• The object’s shape
• The object’s surface area

Question 26

What are 3 things that we can do to maximize the rate of energy transfer?

Answer 26

• Good conductors
• Painted dull black
• Have the air flow around them maximized

Question 27

What are 3 things that we can do to minimize the rate of energy transfer?

Answer 27

• Good insulators
• White and shiny
• Prevent convection currents by trapping air in small pockets.
• -MUST minimize the transfer of energy of conduction, convection and radiation.

Question 28

What is the specific heat capacity?

Answer 28

The amount of energy required to raise the temperature of 1 kg by 1°C.

Question 29

Name the relationship between mass and temperature change.

Answer 29

The greater the mass of an object, the more slowly its temperature increases when it is heated.

Question 30

What three things does the rate of temperature change in a substance depend on?

Answer 30

• Energy transferred to it
• Mass
• Specific heat capacity.

Question 31

What is the formula for specific heat capacity?

Answer 31

E = m x c x θ
Where:
E is energy transferred, J
m is mass, kg
c is specific heat capacity, J/kg°C
θ is temperature change, °C

Question 32

Name 5 things that can minimize the rate of energy transfer out of homes.

Answer 32

• Fiberglass loft insulation to reduce E.T. by conduction.
• Cavity wall insulation, trapping small pockets of air, to reduce E.T by convection.
• Double glazing to reduce E.T. by conduction in windows.
• Draught proofing to reduce E.T. by convection.
• Aluminium foil behind radiators to reflect IR back into room.

Question 33

What is a U-Value?

Answer 33

The rate of energy transfer through a material, per second.

Question 34

What does it mean if a material has a lower U-Value?

Answer 34

That material is a better insulator, as it transfer little energy.