# Physics P1

Ocr gateway, physics P1

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## Moving and storing heat

Heat= a measure of energy

Temperature= measure of hotness

Specific heat capacity tells you how much energy something can store

Energy=mass*specific heat capacity*temperature change

Specific heat capacity is the amount of energy needed to raise the temperature of 1kg of a substance by 1'C

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## Melting and Boiling

You need to put in energy to break the intermolecular bonds

boiling- when you heat a liquid, this heat energy causes particles to move faster and when they overcome the attraction to eachother big bubbles of gas form

When a substance is melting or boiling you are putting in energy but its used for breaking the intermolecular bonds thats why they are flat on graphs

When a substance is condensing or freezing bonds are forming which releases energy

Specific latent heat is the energy needed to change state

equation= Energy= Mass*Specfic latent heat

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## Conduction in the home

Conduction mainly occurs in solids- through windows

Conduction of heat is the process where vibrating particles pass on extra kinetic energy to neighbouring particles

metals are good conductors of heat- why used for sauce pans

non metals are good for insulating things

(good conductors= bad insulators and vise versa)

Air is a good insulator as in liquids and gases heat is conducted slower than in solids as the particles aren't held together as tight

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## Convection in the home

Convection occurs in liquids and gases

when you heat up a liquid or gas the particles move faster and it expands becoming less dense, th warmer less dense fluid rises and cooler fluid takes its place- end up wiith a circulation of convection current- like in an immersion heater

Convection occurs when the more energetic particles move from the hotter region to the cooler region and take their heat energy with them

Radiators in the home rely on convection to circulate warm air around the room

To reduce convection need to stop the fluid moving by using clothes, blankets and cavity wall foam

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Radiation is how we get heat from the sun

Heat is radiated as infra red waves

Its different from conduction and convection

• can occur in a vacuum
• can occur through transparent substances
• the amount of radiation emitted or absorbed depends on its surface colour and texture
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## Emitting and absorbing heat radiation

The hotter an object gets the more heat radiation it emits

Cooler objects absorb the heat radiation from hotter objects around them

matt black surfaces are good absorbers and emitters of radiation

Light- coloured smooth objects are very poor absorber and emmitters of radiation, reflect heat radiation- e.g. pittong shiny foil behind radiators

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Grills and toasters heat food by radiation

• The heat radiated by the grill is absorbed by the surface particles of the food increasing their kinetic energy, this energy is then conducted and convected to more central parts

people often line their grill pan with shiny foil to reflect the heat radiation back onto the bottom of the food being grilled

Over exposure to heat radiation damages body cells and causes burning

Thermograms show where you house is leaking heat

they display different amounts of radiation in different colours

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## Saving energy

Insulating your house saves energy and money

Ways of reducing conduction

• loft insulation
• hot water tank jacket
• double glazing
• cavity walls and insulation
• thick curtains

Ways of reducing convection

• draught proofing
• cavity wall insulation

• thick curtains
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## Efficiency

Machines always waste some energy

More efficient machines waste less energy

Efficiency= Useful Energy Output

Total energy input

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## Electromagnetic Waves

Amplitude= distance from the rest position to crest

Wavelength= length of full cycle of a wave- crest to crest

Frequency= number of complete waves passing a certain point per second

All waves can be reflected, refracted and diffracted

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## Wireless communication

Long wavelengths travel well through the earth's atmosphere- radio waves and microwaves, they don't get absorbed by the earth's surface

Refraction can help radio waves travel furthur as when the wave comes up against something that has a different density it changes speed and if the wave hits the new substance at an angel it changes direction

• UV radiation from the sun creates layers of ionised atoms, these are electrically charges layers called the ionosphere
• radio waves travel faster through ionised parts of atmosphere- leads to refraction
• the amount a wave is refracted in the ionosphere depends on its frequency and angle of elevation
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## Interference

= when you have two or more waves with a similar frequency, when they come into contact they can create one combined signal with a new amplitude

you can get interference when you have two radio stations on similar frequencies

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## Wireless Communications

Diffraction is when waves spread out and bend round corners- can cause signal loss

The amount a wave is diffracted depends on the size of the gap relative to the wavelength of the object

• gap much wider than wavelength- little diffraction
• gap a bit wider than wavelength- diffraction only at edges
• gap same length as wavelength- maximum diffraction
• mobile phone calls travel as microwaves from your phone to the nearest transmitter
• microwaves don't diffract much so the transmitters need to be placed in line of site- usually on hill tops close to each other
• microwaves can be used yo carry satellite TV broadcasts or satellite phone calls
• transmitter on earth sends signal to space
• where it is picked up be a receiver dish and it is transmitted back to earth and picked  up by receiving satellite dish
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## Microwave ovens

Microwave ovens use a different wavelength to mobiles

• microwaves used for communication need to travel through earths atmosphere but microwaves in microwave ovens are absorbed by water molecules in food
• they penetrate a few cm's in before being absorbed by the water molecules increasing their kinetic energy this energy is then conducted or convected to other parts
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## Opitcal Fibres

• carry data over long distances as pulses of light or infra-red radiation
• work by bouncing waves off the sides of a very narrow core
• the light enters at one end and is reflected again and again until it reaches the other end
• very quick to communicate
• made of high purity glass
• Total internal reflection
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## Total internal reflection

Total internal reflection can only happen when the light ray travels through a dense substance like glass, water or perspex

It all depends on the incidence ray

• If the angle of incidence is less than the critical angle most of the light is refracted into the out layer but some is internally reflected
• If the angle of incidence is equal to the critical angle the ray would go along the surface with quite a bit of internal reflection
• If the angle of incidence is greater than the critical angle no light comes out it is all internally reflected- total internal reflection
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## Digital technology

An analogue wave can have any value (shown by a wave)

A digital signal can only take 2 values- on or off

• When analogue is amplified low-amplitude noise is amplified too
• with a digital signal the low-amplitude noise is ignored
• Using digital you can transmit lots of signals at once- multiplexing
• multiplexing happens in phone wires
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## CD players

• use lasers to read digital information
• surface of a CD has shallow pits cut into it and the areas between are called lands
• A laser is shone onto the CD as it is reflected by the shiny surface
• The beam is reflected differently from the troughs and pits and this difference is picked up by a light sensor which can be changed into an electrical signal
• An amplifier and a loud speaker convert the electrical signal into sound of the right frequency and loudness
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• UV rays damage DNA in cells
• melanin in dark skin provides protection against UV radiation by absorbing it so less reaches sensitive layers under the skin
• time= time in sun times SPF factor

The ozone layer protects us from UV radiation

• ozone= O3
• absorbs some of the suns UV radiation
• CFCs containing chlorine have damaged the ozone layer which lets more UV radiation in making it hotter
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## The Environments

Natural events and human activity can also change the climate on a global scale

• changes in the earth's orbit around the sun can help cause an ice age
• CO2 is gradually increasing and decreasing, its increased by human activity- burning fossil fuels and forests being cut down
• The greenhouse effect makes the earth warmer
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## Wave equation

Speed= frequency time wavelength

MAKE SURE UNITS ARE THE SAME

1kHz (kilohertz) = 1000Hz

1MHz (1 megahertz) = 1 000 000 Hz

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## Seismic waves

when there is an earthquake it produces shock waves, these are recorded as seismic waves using seismographs

P- waves= longitudinal, push ground back and forth, travel through liquids and solids, are faster

• can pass through the core
• travel faster through the core showing its solid

S-waves= transverse, only travel through solids, shake from side to side and are slower than P-waves

• are not detected in the core which tells us the outer core is liquid
• they can travel through the mantle telling us it must be solid
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