Heat

Question 1

temperature

Answer 1

a measure of how hot or cold something is
unit: kelvin (K)

Question 2

thermometric property

Answer 2

any physical property that changes measurably with temperature. e.g. length of a column of liquid, electrical resistance, emf of a thermocouple, colour, volume of gas at constant pressure, pressure of gas at constant volume

Question 3

heat capacity

Answer 3

heat energy needed to change the temperature of an object by 1K
Q= CΔθ

Question 4

unit for heat capacity

Answer 4

joule per kelvin (JK^-1)

Question 5

specific heat capacity

Answer 5

heat energy needed to change the temperature of 1kg of that substance by IK
unit = Jkg^-1K^-1
Q=mcΔθ

Question 6

latent heat

Answer 6

heat energy needed to change the state of a substance without a change in temperature
unit = joule (J)

Question 7

specific latent heat

Answer 7

heat energy needed to change the state of 1kg of a substance without a change in temperature
unit = joule per kilogram (Jkg^-1)

Question 8

specific latent heat of fusion

Answer 8

heat needed to change 1kg of a substance from a solid to a liquid

Question 9

specific latent heat of vaporisation

Answer 9

heat needed to change 1kg of a substance from a liquid to a gas

Question 10

conduction

Answer 10

transfer of heat through a substance by molecules vibrating without overall motion of the substance e.g. metals

Question 11

convection

Answer 11

transfer of heat through a liquid/gas by means of circulating currents (convection currents) e.g. sea breezes/radiators

Question 12

radiation

Answer 12

transfer of heat from one place to another in the form of electromagnetic waves e.g. hot objects, sun, human body

Question 13

U-value

Answer 13

amount of heat energy conducted per second through 1m^2 of that structure when a temperature difference of 1 deg. celsius is maintained between its ends

Question 14

Tog value

Answer 14

The tog is a measure of thermal insulance of a unit area, also known as thermal resistance. It is commonly used in the textile industry and often seen quoted on, for example, duvets and carpet underlay. A tog is 0.1⋅m2⋅K/W. In other words, the thermal resistance in togs is equal to ten times the temperature difference (in °C) between the two surfaces of a material, when the flow of heat is equal to one watt per square metre.

Question 15

solar constant/ solar irradiance

Answer 15

average amount of the suns energy falling per second perpendicularly on 1m^2 of the earth’s atmosphere
about 1.35kWm^-2

= power/area
or energy per sec/ area

Question 16

celsius to kelvin

Answer 16

temp. in deg. celsius = temp. in kelvins - 273.15

Question 17

heat pump

Answer 17

transfers energy from a cooler region to a warmer one e.g. fridge

Question 18

heat pump steps

Answer 18

1. liquid of high specific latent heat of vaporisation and low boiling point used
2. when liquid reaches expansion valve pressure drops
3. liquid evaporates taking in latent heat from inside the fridge, cooling the fridge
4. when the vapour reaches the compressor the pressure increases
5. vapour condenses giving out latent heat. this heat is then given off to surroundings at the back of the fridge
6. heat pump transfers energy from a cooler region to a warmer one

Question 19

heat

Answer 19

form of energy
unit = joule