Physics-P1

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Heat

HEAT - measure of ENERGY
Emergy makes the particles gain kinetic energy and change state
Measure on an absolute scale (can't go below zero) in Joules (J)

TEMPERATURE - measure of HOTNESS
Measure of the average kinetic energy of the particles
Measured in degrees celcius or Fahrenheit
Greater the difference in temperature between two places means faster rate of cooling

SPECIFIC HEAT CAPACITY - amount of energy needed to raise the temperature of 1kg by 1 degree
More energy needed to heat substance means more released when it cools

Energy = mass x specific heat capacity x temeperature change 

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Melting and Boiling

When heating a liquid, heat energy is used to make the particles move faster, when enough particles have enough energy to overcome forces of attraction it begins to boil

When a substance is changing state energy continues to go in and is used to break intermolecular bonds but the temperature doesn't raise

(http://www.a-levelphysicstutor.com/images/thermal/LH-step-graph.jpg)

SPECIFIC LATENT HEAT - amount of energy needed to melt 1kg of material without changing the temperature
SLH is different for different materials and different for melting and boiling
Energy = mass x specific latent heat 

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Conduction and Convection

CONDUCTION - process where vibrating particles pass on extra KE to neighbouring particles
Heat flows from HOT to COLD
Metals conduct heat very well because their electrons are free to move
Liquids and gases conduct heat more slowly because particles aren't held together so tightly

CONVECTION - occurs when more energetic particles move from the hotter region to the cooler region 
When liquids or gases are heated the fluid expands, becoming less dense
Warmer, less dense fluid rises above colder surroundings, cooler fluid then takes its place
This created a circulation 
Convection explains how radiators work
To reduce convection you have to stop the fluid moving
Clothes, blankets and cavity wall foam insulation work by trapping pockets of air, the air can't move so the heat has to conduct very slowly

 

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Heat Radiation

RADIATION - heat radiated as infrared waves (EM waves) in straight lines at the speed of light
Different from conduction and convection because:
1) Doesn't need a medium to travel through - can occur in a medium
2) Only occurs through transparent substances (glass, air, water)
3) Amount of radiation absorbed or emitted depends on surface colour and texture

ALL objects EMIT and ABSORB radiation
Hotter object = more heat radiation emitted
Cooler object = absorbs heat radiation emitted by hotter thing

Matt and black surfaces are the best at absorbers and emitters
Light-coloured, smooth surfaces are very poor

Heat radiation in cooking

Grills and toasters heat food by infrared radiation
Heat radiated by a grill is absorbed by the surface of food particles which increases their KE
Heat energy is then conducted or convected to more central parts 

Microwaves use a different type of EM wave (microwave)
Microwaves penetrate around 1cm of the food  where they're absorbed by water or fat molecules, increasing KE
Energy is then also conducted or convected 

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Saving Energy

Things that emit energy = sources (radiators)
Things that transfer/waste energy = sinks (windows)

PAYBACK TIME - time it takes to save money on energy bills equal to initial cost
Initial cost / annual saving

Loft insulation - fibreglass wool laid on loft floor reduces CONDUCTION through the ceiling
Hot water tank jacket - reduces CONDUCTION
Cavity wall insulation - two layers of bricks with insulating foam squirted into the gap, traps pockets of air, reduces CONVECTION
Draught proofing - reduces CONVECTION
Thick curtains - reduces CONDUCTION and RADIATION through windows
Double glazing - two layers of glass with an air gap, reduces CONDUCTION

THERMOGRAMS - picture taken with thermal imaging camera
HOTTER PARTS = white, yellow and red
COLDER PARTS = dark blue and purple

Objects at different temperatures emit infrared rays of different wavelengths so thermograms display these different wavelengths as different colours 

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Efficiency

Some energy is ALWAYS wasted
Total energy output is always the same as the energy input, but only some energy output is useful
Input energy is always lost or wasted, usually as head energy
Less energy that is wasted, more efficient the device is

EFFICIENCY = USEFUL energy output / TOTAl energy input x 100(http://www.bbc.co.uk/staticarchive/ef1765b78bf7df43639092d398d58b646138287b.gif)

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Wave Basics

AMPLITUDE - displacement from rest position to the crest
WAVELENGTH - length of a full cycle of the wave eg. crest to crest
FREQUENCY - number of complete cycles per second (Hz)

WAVE SPEED = FREQUENCY (Hz) x WAVELENGTH (m)

CONVERTING UNITS:

1 kHz = 1000 Hz
1MHz = 100 000 Hz

 

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Reflection

REFLECTION
Allows us to see objects
Beam of light reflects from uneven surface, light reflects off at different angles
Beam of light reflect from even surface, lights reflected all at same angle, clear reflection

LAW OF REFLECTION:
Angle of indice = angle of reflection 

TOTAL INTERNAL REFLECTION
Can only happen when light travles through a dense material towards a less dense material
If the angle of incidence is big enough, the ray doesn't come out substance at all, reflects back into material
Big enough angle = bigger than the critical angles

(http://www.bbc.co.uk/staticarchive/65349aebb97d347429bfe1623d6ebd6cdb92d7f2.gif) 

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Diffraction and Refraction

DIFFRACTION - waves spreading out
Amount of diffraction depends on the size of the gap relative to the wavelength of the wave
Narrower gap (about the size of wavelength) or longer wavelength = more diffraction 
If a gap is about the same size as the wavelength then you get a diffraction pattern of light and dark fringes

(http://www.bbc.co.uk/staticarchive/31d29a61aab276481d40a6f7faa903eb36a59af3.jpg)

REFRACTION - changing the spped of a wave causing a change in diraction
If a light wave hits a boundary at a straight angle then there will be no change in direction
If a light wave hits a boundary at an angle then part of the wave hits the denser layer first and slows down whilst another part carries on going straight at the faster speed causes a change in direction

 

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EM Waves and Communication

Radio waves, microwave, infrared, visible light, ultraviolet, x-rays, gamma rays (remember the song)
Increasing frequency and decreasing wavelength

EM waves at the end of the spectrum tend to be able to pass through material but ones in the middle are usually absorbed
Higher frequencies (x-rays) tend to be more dangerous to living cells, have more energy
When EM radiation is absorbed is can cause heating and ionisation

Different types of signals:
1) Light, radio and electrical signals can travel really fast
2) Electrical wires and optical fibres can carry lots of information quickly and secure as they can't be tapped into inside a wire but cables can be difficult to repair
3)  Radio signals, intercepted more easily than wires as they travel through the air, issue of wireless internet networks but are easy to repair and also portable

(http://eucard-old.web.cern.ch/eucard-old/activities/communication/public/Images/Spectrum.jpg)

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Communicating with Light

An on-off code being flashed can relay a message over a long distance quickly - Morse code

More modern use of light for communication is optical fibres which carry data over long distances as pulses of light or IR, they bounce of the sides of a narrow core which is protected by outer layers

The ray of light enters so it hits the boudary between the core and outer layer at an angle GREATER than the critical angle, causing TOTAL INTERNAL REFLECTION off the ray within the core
Optical fibres are increasingly used for telephone and broadband cables as well as madical purposes

Using light is very quick and multiplexing means lots of different signals can be sent at once, and because it's digital there's little interference

(http://s.hswstatic.com/gif/fiber-optic-transmission.gif) 

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Lasers

Normal visible light is a combination of waves at different frequencies and wavelength, that are out of phase

Laser beams have all waves at the same frequency and wavelength (MONOCHROMATIC) the waves are all in phase - the troughs and crests line up - increasing amplitude and producing an intense beam
The waves are coherent becuase they have a fixed phase difference (zero, because they are in phase)
Lasers have low divergences - the beam is narrow and stays narrow even at a long distance from the source

CD Players - use lasers to read digital information

Surfaces of CDs have a pattern of billions of shallow pits cut into it, areas between pits are lands
A laser shone onro the CD is reflected from the shiny bottom surface as it spins around
Beams are reflected from a land and a pit slightly differently, difference is picked up by a light sensor
Pits and lands do NOT represent the ons and offs, the change in the reflected beam reperesent on and no change represent off
An aplifier and a speaker then convert the electrical signal into sound of the right pitch and loudness

(http://www.madehow.com/images/hpm_0000_0001_0_img0072.jpg) 

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Infrared

Uses of infrared:
-Cooking (grills and toasters)
-Remote controls to transfer info from TVs and DVD players
-Transmit info between mobiles and computers
-Sensors for security systems
-Carry info through optical fibres (replace visible light)

Infrared radition = heat radiation
Given out by hot objects, more heat means more IR
IR can be used to monitor temperatures, like heat loss through a house's roof
IR is detected by night-vision equipment and displayed on a screen, police and military use this to spot people

Infrared radiation = control electrical equipment
Remote controls emit pulses of IR to control TVs and DVD players
Pulses act as a digital on/off code, the device will detect and decode the pattern and follow the instruction
IR signals are used in the same way to transfer info between mobiles and computers, but only over short distances because the IR beam from a small, low-powered remote is fairly weak
The beam also has to be exactly pointing at the device, IR waves only travel in straight lines 

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Radio Waves

Radio waves and microwaves are good at transferring info over long distabnces because they don't get absorbed by the Earth's atmosphere becuase of their long wavelength and low frequency

Radio waves = communications
Long-wave radio waves cna be transmitted from one place to another around the world because they diffract around the curved surface of Earth
Medium-wave radio signals can reflect from the ionsphere depending on atmospheric conditions
Short-wave radio signals can be received at long distances because of reflection in the ionsphere 
Very short-wave radio signals must be in direct sight of the transmitted, they don't bend

Signal strength depends on diffraction
Amount of diffraction depends on length of wave relative to the size of the gap/obstacle
Longer wavelengths encounter a lot of diffraction because they are large compared to the obstacle
This means they can bends around corners or hills
Shorter wavelength transmitters need to be higher up because they can't diffract as much to avoid obstacles
(http://www.frankswebspace.org.uk/ScienceAndMaths/physics/physicsGCSE/bytesize%20images/radiowaves1.gif) 

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Wireless Communication

Refraction - helps radio waves travel faster 
UV radiation creates the ionsphere in the atmosphere, radio waves travel faster through the ionsphere than non-ionised parts, short and medium waves are reflected back by the ionsphere so they're received further away
The amount of refraction depends on the waves frequency and angle of elevation
Medium waves refract more than short waves

Digital Audio Broadcasting (DAB) compresses signals and sends them as one wave - multiplexing
They are transmitted across a relatively small frequency bandwith and seperated out by receivers
Suffers less interference than analogue because many stations can be broadcast at the same frequency
(http://www.tpub.com/neets/book10/NTX2-17.GIF) 

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Microwaves

Microwaves - satellite communication
Signal from a transmitter is transmitted into space, received by a satellite receiver dish and then transmitted back to a different location on Earth

Mobiles phone calls travel as microwaves from your phone to the nearest transmitter which passes the signal on
Microwaves have shorter wavelengths than radio waves so they don't diffract as much, can't bend around Earth
Microwaves are blocked more by large obstacles like hill because they can't bend around them
Microwave transmitters need to be positioned in line of sight of each other
Microwave are partially absorbed by water even though they can pass through the atmosphere
In bad weather or near lakes, signals can be lost due to absorption or scattering

Mobiles...dangerous?
If microwaves are absorbed by water molecules in living tissue, cells may be burned or killed
Some people think microwaves emitted by phones could damage your healthy
But there is no conclusive proof

(http://www.bbc.co.uk/staticarchive/0670392c132dad7a0372d56dbd852c14974c2e4c.gif) 

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EM Receivers

Minimum size receiver depends on the wavelength of wave being received
Radiowaves need the biggest receiver, then micorwaves etc
When a wave enters a receiver it passes through a gap, if the wave is diffracted it spreads out and detail's lost
So the bigger receiver compared with wavelength means the less diffraction it causes and clearer info

Telescopes - detect different types of EM waves
Different telescopes are used to collects different EM waves, bigger telescopes give better resolution (less diffr)
Since radio waves can be so much bigger than light waves, rdiculously big receivers would be needed so scientists make do with a lower resolution
Radio telescopes are often linked together and signals combined to increase resolution
Optical microscopes have to be small making it hard to get a good resolution - diffraction limited

(http://www.srt.inaf.it/static/img/parallax/1.png) 

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Analogue and Digital Signals

To communicate any kind of information it has to be converted into electrical signals which can be analogue or didgital

ANALOGUE SIGNALS:
Takes any value between a certain range
Amplitude and frequency continously varies
When amplified signal loses quality

DIGITAL SIGNALS:
Takes only two values, ON or OFF
Signal remains high quality over distance, easy to ignore/remove interference
Transmit several signals at the same time
MULTIPLEXING - different signals are sent and then seperated out again at the other end
(http://jhigh.co.uk/ComputingSG/Images/Graphics/AutoSystems/analogueDigitalGraph.gif) 

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CFCs

Ultraviolet radiation - damages DNA in cell, increases risk of skin cancer
Darker skin gives more protection as it absorbs more UV radiation, prevents radiation reaching more vulnerable cells

Ozone layer - O3 atoms - absorbs some of the UV rays
CFCs - react with oxygen breaks the O3 up, making the ozone thinner

Antartica winter - weather effects concentration of ozone to drop dramatically
Low concentration means a hole in the ozone layer
Scientists have to monitor it to understand why it's happening and how to prevent it 

CFCs - BANNED INTERNATIONALLY

 

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Seismic Waves

Earthquakes - two different types of seismic waves produced

P-Waves - Longitudinal - Vibrate side to side
Travel through SOLIDS and LIQUIDS

S-Waves - TranSverSe - Vibrate up and down
Travel through Solids and Slower than P-waves

About halfway through the Earth, P-waves change direction which shows the sudden change in properties
S-waves are not detected in the core's shadow so the outer core must be liquid
P-waves travel faster through the middle so inner core must be solid
S-waves travel through mantle so must be solid

(http://www.frankswebspace.org.uk/ScienceAndMaths/physics/physicsGCSE/bytesize%20images/earthStrucHigher1.gif) 

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