p1 physics revision

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Heat

Heat is a measure of energy 

When a substance is heated it gains energy 

energy makes the particles in a gas or liquid move faster

in a solid particles vibrate heat energy is measured in joules 

Tempreture is a measure of hotness measured in degrees celsius 

if things have different tempretures heat energy will flow between them flowing from hot objects to cooler objects

rate of cooling depends on differnce in tempreture between a hot object and its surroundings the hotter the object is compared to surroundings the faster it looses heat

Thermograms show tempretures

hot parts white yellow and red

cold parts black dark blue and purple 

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specific heat capacity

specific heat capacity tells us how much energy stuff can store 

amount of energy depends upon mass and the materials its made from 

specific heat capacity is the amount of energy needed to raise the tempreture ok 1kg of a substance by 1degree celsius 

to work out specific heat capacity of substances:

measure amount of energy added

tempreture change 

Energy=massxshcxtemp change 

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Melting and boiling points

You require energy to melt or boil something :

tempreture rises until you reach the melting point 

the tempreture keeps rising until the solid has changed state into a liquid 

at boiling point all the liquid changes state into a gas 

Energy is given out during freezing:

energy is given out when a gas changes to a liquid (condensing)or a liquid to a solid(freezing)

tempreture doesnt decrease until all substances have changed state 

Specific latent heat: energy=massxslh

is the amount of energy needed for a material to change state 

slh of melting=amount of energy to melt 1kg without changing its tempreture 

slh of boiling =energy neede to boil 1kg of material without a change in tempreture 

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Conduction and convection in the home

Conduction happens mainly in solids 

in a solid particles are held tightly together

when particles vibrate they bump into other nearby particles

Heat conduction is where vibrating particles pass on extra energy to other particles 

this makes heat spread all the way through the solid 

Air is a good insulator 

liquid and gasses arent held so tightly together this stops them bumping eachother 

a good insulator doesnt conduct heat very well this means air(gas)is a good insulator

good conductors are bad insulators 

metals are good conductors of heat 

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continued....

convection happens in liquids and gasses

convection is when particles with more energy move from a hot place to a cooler one taking heat energy with them 

the warmer fluid rises above the cooler parts

as the warm part rises the cooler fluid falls and a circular flow of fluid called a convection current is formed

convection cant happen in solids as particles cant move

tos top convection you have to stop liquid or gas moving 

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Heat radiation

All objects emit and absorb heat radiation 

heat is radiated as infared radiation 

you can feel heat radiation by warmth eg the sun

objects can emit and absorb heat radiation

the hotter an object the more it emmits

cooler objects absorb heat radiation from hotter objects

when heat radiation is present the tempreture rises 

Heat radiation is essential in cooking by infared radiation in toasters and grills 

heat is radiated by a grill and absorbed by a surface particles of the food 

heat is then conducted or convected in the middle parts and reflects heat back onto the bottom of the food being grilles to cook more easily 

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Saving energy

Insulation saves energy and essentially money

things that emit energy are called sources eg radiators

things that use and waste or loose energy are called sinks eg windows and computers

insulation saves energy saving money

sinks are more efficent at their job they waste less enrgy

PAYBACK TIME=INITIAL COST+ANUAL SAVING

most insulation traps air and to stop heat being lost you need to reduce conduction and convection and radiation 

conduction and convection can usually be reduced by trapping air as air is a good insulatorr and poor conductor 

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loft insulation and cavity wall insulation

loft insulation:

a thick layer of fibre glass laid accross the loft and floor ceiling reduces heat loss by conduction and convection traps air consequently a good insulator 

cavity wall insulation two layers of bricks with a gap between them reduces conduction insulating foam or fibre glass is added to reduce convection 

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efficiency

Machines always waste some energy 

machines change energy one from another like chemical energy in a car

total enrgy out=total energy put in energy is always conserved

some is useful energy other energy is wasted into heat and sound energy 

efficency=usefulenergy output/total energy input(x100%)

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Snaky diagrams

The thickness of the arrows show the amount of energy 

The sankey diagram shows energy transformation and how much is useful energy and how much is wasted energy 

total in=total out

Total input=useful +wasted energy 

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wave basics

Waves have amplitudes wavelength and frequency 

amplitude=distance from rest to crest

wvelength =form crest to crest

frequency=number of complete waves

measured in hertz 

Wave speed =frequencyx wavelength

speed=frequencyx wavelngth 

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Wave properties

all waves can be reflected and refracted and even diffracted!!!!!!

all electromagnetic waves travel in a straight line 

when waves meet an obstacle they may change direction

this can happen by refraction reflection and diffraction 

Reflection=lets us see things

light bounces off an object into your eyes

for every reflected ray the angle of incidence =angle of reflection 

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continued....

diffraction waves spreading  out 

changing the gap affects how much it diffracts 

Refraction changing the speed of a wave can change its direction 

different substances have different speeds

change in speed can make the wave change direction 

light waves when they meet a boundary at an angle will refract 

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Em waves and communication

Seven types:

radio waves

microwaves

infared

visible light

ultra violet

x rays gamma rays 

Some EM waves are used to send messages such as radios by tv and radio transmissions radars 

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continued .....

The size of the reciever is depandant upon the size of the wave 

size of the reciever is linked to the wavelngth of the wave

the longer the wavelength the larger the reciever should be 

radio waves are the biggest recievers then infared the light waves ect

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Communicating with light and infared

communication with light needs a code 

morse code was often used for flashing a light on and off to communicate in a code 

they had ...... and ///// 

pulses of light last for a certain length

a type of digital signal 

Lasers produce narrow beams of single coloured light 

a laser beam is just a special ray of light

light waves in a laser are one single colour 

monochromatic 

narrow beams 

intense enrgy beams 

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continued .....

infared has many uses around the home 

mobile phones/computers but only short distances

Ir signals can control electrical equipment as remote controlls work by flashing pulses of light of ir in different patterns 

pulses act as codes similar to morse code 

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optical fibres

total internal reflection depends on the critical angle 

below the critical angle the ray refracted internally reflected for some 

at the critical angle ray along the surface 

above the critical angle the ray doesnt come out internally reflected 

Light and infared can travel through optical fibres

optical fiibres carry data  over long distances pulses of light 

enters fibre at bigger than the critical angle 

causes total internal reflection within the fibre 

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Wireless communication

wireless technology uses electromagnetic radiation for communication without wires

used in phones and printers

however you do require an ariel its convienient portable and no wires needed

All waves can be reflected and refracted:

waves used for communication are always meeting obstacles but different substances can mean they reflect or refract

which is good for communication purposes 

as they can travel long like radio waves 

can be a bad thing as refraction can bend signals away from recievers so signal lost 

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radio and digital waves

a radio station sends radio waves of a certain frequency 

different stations send out similar frequencies

some waves are often interfered when you hear two signals it can be unpleasnt so radio stations near often use different frequencies 

Digital radio helps reduce interference but cant pick up dab and sound quality of DAB isnt as good as analogue fm 

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Microwaves

microwaves carry mobile phone signals to the nearest transmitters

they dont diffract

transmitters need to be in line of sight 

Microwave ovens use a different wavelength from mobiles 

Microwaves penetrate few centimetres into food 

abosrbed by water or fat molecules which heats them 

heat energy then conducted or convected to other parts 

can pass through glass 

reflected by shiny metals 

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Analogue and digital signals

information is changed into signals (electrical signals)

they are either analogue or digital

Analogue signals vary

digital signals are just on or off 

digital signals can be better than analogue as all signals pick up noise when they travel long distances 

its easier to remove noise from digital than analogue signals 

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Humans and the environment

Ultraviolet radiation causes skin cancer 

sunburn can be as aresult of a long period of time in the sun but more uv damages cells 

darker skins have more protection due to the melanin in the skin as uv is absorbed more and reaches less deeper cells 

the higher the sun cream factor the more protection

Sunbeds are a big no because they concerntrate uv rays deep into your cells that damages them and as a result can cause skin cancer

There is a hole in the o zone layer over antartica 

as uv rays from the sun reduce uv reaching earth so protects us from harm but antartica is dropping ozone levels unexpectedly and this means it looks like a hole 

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Seismic waves

Earthquakes cause seismic waves they travel both on the surface and inside earth shock waves are detected be seismometers and recorded on graphs 

two different types of seismic waves include p waves and s waves 

p waves are longitudal travel through solids and liquids 

faster than s waves

s waves are transverse 

only travel through solids 

slower than p waves 

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