p1 physics revision
- Created by: Eleanor200101
- Created on: 21-02-17 14:57
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
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
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
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
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
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
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
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
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%)
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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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