Energy transfers by heating

Question 1

thermal conductivity

Answer 1

the thermal conductivity of a material tells you how quickly energy is transmitted through my thermal conduction

Question 2

how can you test thermal conductivity?

Answer 2

you can test the thermal conductivity of rods made of different metals:
each rod must have the same diameter + length + same temperature difference between its ends
one on each rod is covered in wax and the other ends are heated equally.
The faster the wax melts, the higher the thermal conductivity of the metal

Question 3

heating bills can be expensive…

Answer 3

heating bills can be expensive so it is important to reduce the rate of heat loss from buildings.

Question 4

what are the factors affecting the rate of heat loss from a building?

Answer 4

1. the thickness of its walls and roof
2. the thermal conductivity of its walls and roof

Question 5

lower thermal conductivity = …

Answer 5

lower thermal conductivity = lower rate of heat losswhat can the thermal conductivity of the walls and roof be reduced by?

Question 6

what can the thermal conductivity of the walls and roof be reduced by?

Answer 6

the thermal conductivity of the walls and roof be reduced by thermal insulators

Question 7

what’s a thermal insulator?

Answer 7

a thermal insulator is a material which has a low thermal conductivity.

Question 8

whats the rate of energy transfer through an insulator?

Answer 8

the rate of energy transfer through an insulator is low.

Question 9

what does the energy transfers per second depend on?

Answer 9

1. the material’s thermal conductivity
2. the temperature difference between the 2 sides of the material.
3. the thickness of the material

Question 10

When a substance is heated or cooled the temperature change depends on….

Answer 10

the substance’s mass
the type of material
how much energy is transferred to it

Question 11

What type of capacity does every type of material have?

Answer 11

specific heat capacity

Question 12

specific heat capacity

Answer 12

the amount of energy needed to raise the temperature of 1kg of a substance by 1°C.

Question 13

how can energy being transferred to the thermal store of a substance be calculated?

Answer 13

the energy transferred to the thermal store of a substance can be calculated from the substance’s:
mass
SHC
temperature change

Question 14

state the equation for the change in thermal energy.

Answer 14

∆E = m c ∆θ

∆E = change in thermal energy (J)
m = mass (kg)
c = SHC (J/kg°C)
∆θ = temperature change (°C)

Question 15

infrared radiation is…

Answer 15

infrared radiation is a part of the electromagnetic spectrum

Question 16

what do all objects do in terms of infrared radiation?

Answer 16

all objects emit and absorb infrared radiation.

Question 17

what does it mean for the infrared radiation if there’s a high temperature of an object?

Answer 17

the higher the temperature of an object, the more infrared radiation it emits in a given time.

Question 18

a good absorber of infrared radiation is = ?

Answer 18

a good absorber of infrared radiation is also a good emitter

Question 19

for an object at a constant temperature:

Answer 19

infrared radiation emitted = infrared radiation absorbed
infrared radiation is emitted across a continuous range of wavelengths

Question 20

what would happen to an objects temperature if it absorbs infrared radiation at a higher rate than it emits it?

Answer 20

an objects temperature will increase if it absorbs infrared radiation at a higher rate than it emits it. this rule applies to the planet earth

Question 21

whats a “black body”?

Answer 21

a black body is a theoretical object that absorbs 100% of the radiation that falls on it.

Question 22

what would a perfect black body do?

Answer 22

a perfect black body would not reflect or transmit any radiation. and would also be a perfect emitter of radiation.

Question 23

what are some factors that the temperature of the earth depends on?

Answer 23

the temperature of the earth depends on lots of factors including:
the rate of which visible light are:
reflected
absorbed
and emitted
by the Earth’s atmosphere and surface.

Question 24

describe how greenhouse gases take part in increasing the temperature on earth.

Answer 24

1. GH gases absorb infrared radiation emitted by the surface of the earth —- prevent it escaping into space
2. they then re-emit the infrared radiation back towards the surface of the earth —– increasing the earths temperature.

Question 25

what gases are known as the greenhouse gases?

Answer 25

water vapour
methane
carbon dioxide

Question 26

what increases the amount of greenhouse gases in the earth’s atmosphere?

Answer 26

human activities:
burning fossil fuels
deforestation
livestock farming

Question 27

what can an increase in the earth’s temperature cause?

Answer 27

an increase in the earth’s temperature leads to a major cause of climate change