P1

Front 1

P1 Heating houses

Back 1

Heat energy is needed to increase the temperature of an object. The amount of energy depends on the mass of an object, the type of material it is made from and the temperature increase.

Front 2

P1 Heating houses

Back 2

Heat energy is also absorbed when substances melt or boil, the temperature does not alter during a change of state. The amount of energy needed to melt or boil something depends on the mass of the object and the type of material it is made from.

Front 3

P1 Temperature

Back 3

Temperature and heat are not the same thing because:
temperature is a measure of how hot something is
heat is a measure of the thermal energy contained in an object.
Temperature is measured in ºC, and heat is measured in J.

Front 4

P1 Thermograms

Back 4

Thermal imaging cameras can detect infrared radiation - the type of radiation emitted by all objects. The images they produce are called thermograms.

Front 5

P1 Thermograms

Back 5

False colours are added to a thermogram to give an indication of how hot each object in the image is, with:
The hottest parts coloured white, yellow or red
the coldest parts are coloured purple, dark blue or black

Front 6

P1 Changing temperatures

Back 6

Heat energy flows from a hot object to a cooler one. This causes:
hot objects to cool down
cool objects to warm up.

Front 7

P1 Changing temperatures

Back 7

When heat energy is transferred to an object, its temperature increase depends upon:

the mass of the object
the substance the object is made from
the amount energy transferred to the object.

For a particular object, the more heat energy transferred to it, the greater its temperature increase

Front 8

P1 Specific heat capacity

Back 8

The specific heat capacity of a substance is a measure of how much heat energy it can hold. It is the energy needed to increase the temperature of 1 kg of the substance by 1 ºC. Different substances have different specific heat capacities.

Front 9

P1 Heat capacity of substances

Back 9

Notice that water has a particularly high specific heat capacity. This makes water useful for storing heat energy, and for transporting it around the home using central heating pipes.

Front 10

P1 Changing state

Back 10

A substance must absorb heat energy so that it can melt or boil. The temperature of the substance does not change during melting, boiling or freezing, even though energy is still being transferred.

Front 11

P1 changing state

Back 11

A heating curve is a graph showing the temperature of a substance plotted against the amount of energy it has absorbed. You may also see a cooling curve, which is obtained when a substance cools down and changes state.

Front 12

P1 Specific latent heat

Back 12

The specific latent heat of a substance is a measure of how much heat energy is needed to melt or boil it. It is the energy needed to melt or boil 1 kg of the substance.

Front 13

P1 Specific latent heat

Back 13

Different substances have different specific latent heats. The specific latent heat of a given substance is different for boiling than it is for melting. The table shows some examples.

Front 14

P1 Specific heat capacity

Back 14

The equation relating energy to specific heat capacity:
energy (J) =
mass (kg)×specific heat capacity (J/kg/ºC)×temperature change (ºC)

Front 15

P1 Specific latent heat

Back 15

the equation relating energy to specific latent heat:
energy (J) =
mass (kg) ×Specific latent heat (J/kg)

Front 16

P1 Changing state

Back 16

The temperature does not alter during melting and boiling. This is because the energy is used to break the bonds between the particles in the substance.

Front 17

P1 Conduction

Back 17

Heat is thermal energy. It can be transferred from one place to another by conduction, which involves particles.

Front 18

P1 Conduction

Back 18

Metals are good conductors of heat, but non-metals and gases are usually poor conductors of heat. Poor conductors are called insulators. Heat energy is conducted from the hot end of an object to the cold end.

Front 19

P1 Conduction

Back 19

The electrons in a piece of metal can leave their atoms and move about in the metal as free electrons. The parts of the metal atoms left behind are now charged metal ions. The ions are packed closely together and they vibrate continually. The hotter the metal, the more kinetic energy these vibrations have. This kinetic energy is transferred from hot parts of the metal to cooler parts by the free electrons. These move through the structure of the metal, colliding with ions as they go.

Front 20

P1 Convection

Back 20

Heat can be transferred from one place to another by convection. Like conduction, the process involves particles.

Front 21

P1 convection

Back 21

Liquids and gases are fluids because they can be made to flow. The particles in these fluids can move from place to place. Convection occurs when particles with a lot of heat energy in a liquid or gas move and take the place of particles with less heat energy. Heat energy is transferred from hot places to cooler places by convection.

Front 22

P1 convection

Back 22

Liquids and gases expand when they are heated. This is because the particles in liquids and gases move faster when they are heated than they do when they are cold. As a result, the particles take up more volume. This is because the gap between particles widens, while the particles themselves stay the same size.

Front 23

P1 convection

Back 23

The liquid or gas in hot areas is less dense than the liquid or gas in cold areas, so it rises into the cold areas. The denser cold liquid or gas falls into the warm areas. In this way, convection currents that transfer heat from place to place are set up.

Front 24

P1 Heat transfer by radiation

Back 24

Heat can be transferred by infrared radiation. Unlike conduction and convection, which need particles, infrared radiation is a type of electromagnetic radiation that involves waves.Heat can be transferred by infrared radiation. Unlike conduction and convection, which need particles, infrared radiation is a type of electromagnetic radiation that involves waves.

Front 25

P1 Heat transfer by radiation

Back 25

Radiation can even work through the vacuum of space. This is why we can still feel the heat of the Sun even though it is 150 million km away from the Earth.

Front 26

P1 Different surfaces

Back 26

Some surfaces are better than others at reflecting and absorbing infrared radiation. The table summaries some differences.

Front 27

P1 Different surfaces

Back 27

If two objects made from the same material have identical volumes, a thin, flat object will radiate heat energy faster than a fat object. This is one reason why domestic radiators are thin and flat. Radiators are often painted with white gloss paint. They would be better at radiating heat if they were painted with black matt paint, but in fact, despite their name, radiators transfer most of their heat to a room by convection.

Front 28

P1 Efficiency

Back 28

The efficiency of a device is the proportion of the energy supplied that is transferred in useful ways. You should be able to calculate the efficiency of a device as a decimal or as a percentage.
The efficiency of a device can be calculated:
efficiency = useful energy out ÷ total energy in (for a decimal efficiency)
efficiency = (useful energy out ÷ total energy in) × 100 (for a percentage efficiency)

Front 29

P1 Payback time

Back 29

Home owners may install double glazing or extra insulation to reduce heat energy losses and so save money. However, these energy-saving solutions cost money to buy and install. The payback time of an energy-saving solution is a measure of how cost-effective it is. Here is the equation to calculate payback time:
payback time (years) = cost of installation (£) ÷ savings per year in fuel costs (£)
The payback time will be shortest if the cost of installation is low compared to the savings made each year.