Temperature vs heat

• If something has a high temperature, it is hot and will cool down to room temperature

• Temperature is measured in degrees Celsius

• If something has a low temperature it is cold and will eventually warm up to the temperature of the room surrounding it

Temperature vs heat

• Heat is a form of energy

• Heat is measured in joules (J)

• Heat can be stored in an object – road surfaces in summer or the sea

• Heat is a measure of total internal energy

Changes of state

• Solid liquid gas

• What do the particles look like at each stage?

Heat is required to make the changes between the states

Melting point Boiling point

Latent heat = heat needed to change a state without a change in temperature

Specific heat capacity

• Objects get heated and their temperature rises energy is transferred

• The amount of heat needed to change the temperature depends on the material of the objects

Specific heat capacity

1.Which substance has the highest specific heat capacity?

2.How many joules of energy would be needed if you had 2kgs of mercury?

Specific heat capacity

Specific heat capacity = mass x specific heat capacity x temperature change

Calculate the energy transferred when 80kg of

water in a tropical freshwater fish tank is

heated from 10 C to 25 C. The specific heat capacity

of water is 4200J

Energy transferred = 80 x 4200 x (25-10)

Energy transferred = 80 x 4200 x 15

Energy transferred = 5040000J = 5040kJ

Specific latent heat capacity

• Energy needed to change the state of a substance but without a change in temperature

• Depends on the material that the object is made from

• Energy transferred even thought there is no temperature change

Video on page 186

Conduction• When particles get hot they move more quickly• If something is a conductor, heat can travel through the

object• Metals are conductors• The opposite of a conductor is an insulator• Heat travels from hot areas to colder areas

Convection

• When gas is heated it expands (spreads out)• Hot air/liquid rises and as it rises away from the heat

source, it cools and drops back to the heat source• This does not happen in a solid as particles CANNOT

move• This is how a radiator works – heat moves up from the

radiator becoming less dense (less thick), cools and then becomes more dense (thicker), dropping back down to the floor

Radiation

• Radiation is heat energy

• Infrared radiation from the sun is reflected from shiny surfaces – the heat is then used for cooking and heating

• Infrared radiation is absorbed by black surfaces

• Infrared radiation is reflected from shiny surfaces

Black cars are normally a lot hotter than white cars in summer!

To start…

Convection, conduction and radiation in housing

Pay Back Time

• You can reduce energy loss from your home by insulated your house.

• This can be expensive so to work out how cost effective a certain form of insulation is we use the idea of PAY BACK TIME

• This is how long it takes you to get your money back before you go into profit

• Payback time= cost of insulation/annual saving

Pay Back Time Calculation

• Eg• Cavity wall insulation costs £250, it saves

£125 per year (annual saving). What is the Pay Back time for the cavity wall insulation?

• Loft insulation costs £400 and saves £150 per year. Which is the best insulation to install if

• A) You’re staying in the house for 3 years?• B) You’re stopping for 5 years?

Inside the walls, cavity wall space can be filled with foam.

Foam can also be injected into the gap in the walls. This

prevents heat loss.

Insulate the roof so that heat is not lost through the ceiling and

roof of the house.

Fibreglass wool or similar is used because it has small holes in that trap air and insulate the house.

Aluminium foil is sometimes added behind radiators to reflect

the heat

Closing curtains and double glazing is an easy way of

reducing energy loss

Fires can be energy inefficient. Heat is lost easily.

The position of the fire is important and fans can be

brought to push the heat away from the fire so it isn’t lost up the

chimney.

Putting draught excluders under doors prevents heat loss

Transverse waves

• Particles go up and down in transverse waves

• Different parts of the wave show different things

http://www.bbc.co.uk/schools/gcsebitesize/science/edexcel_pre_2011/waves/anintroductiontowavesrev2.shtml

(String demo)

Labelling a wave• Collect a sheet showing a transverse wave – don’t worry if

you get it wrong…we will green pen it!!

Label the wave with descriptions below:

• Amplitude is the maximum movement of a particle from a rest position

• Wavelength is the distance between 2 of the same points on a wave – the unit of wavelength is metres

• Crest is the top of the wave

• Trough is the bottom of a wave

• The rest position is the line that the wave sits onCheck your diagram and CORRECT in green. Add

descriptions too…

Trapped light

• Light is able to stay inside a material – water, Perspex and glass

• The light is reflected if the material is denser than air. This happens on the boundary of the material

• Called total internal reflection

• Example – optical fibres

To start…

• Microwaves are part of the electromagnetic spectrum – but where are they found?

A

B

C

The correct answer is C. Microwaves are found next to infrared and after radiowaves!

Microwave cooking

• Microwaves penetrate food about 1 cm into the outer layers and are fast at cooking food

• Microwaves can pass through glass and plastic but are reflected off shiny surfaces

• Door of a microwave is special glass – reflects the waves back into the microwave

Infrared cooking

• ALL warm objects emit heat radiation – you are right now!

• If an object is hotter, it will give out more radiation

• Infrared rays are absorbed only by surface particles

Infrared radiation can be absorbed or reflected – what colours do you think will absorb and which will reflect?

Mobile Phones

• Microwaves are used to transmit mobile phone cells

• Your mobile phone therefore has a microwave transmitter and receiver of microwaves

• Microwaves can reflect off large surfaces (like water) and be spread out – what effect do you think they might have on our signal?

Ultraviolet C

• absorbed/reflected by atmosphere • germicidal properties• germicidal lamps.

Ultraviolet B • some is absorbed in the atmosphere• causes DNA damage• tanning, burning and aging . Ultraviolet A• penetrate into skin surface• damages DNA• light tanning• deep penetration can cause skin cancer.

Some useful uses of ultra violet light…

Skin cancer cause and prevention

• Around the room is information about skin cancer

• You need to use the information to fill in your worksheet

• You will need the information later so make sure you take note of the main points – DO NOT COPY, you don’t have time…