# WAVES

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• Created by: florrie
• Created on: 23-01-19 09:22

## WAVES DEFINITION

TRANSVERSE = the oscillations are perpendicular to the direction of energy transfer, not all trasnverse waves require a medium

LONGITUDINAL = the oscillations are parallel to the direction of energy transfer, require a medium to travel in

AMPLITUDE = is the maximum dispacement of a point on a wave away from its undisturbed position

WAVE LENGTH = distance from a point on one wave to the equivalent on the adjacent wave (measure from rarefraction to another rarefraction or compressions in longitudinal)

FREQUENCY = number of waves passing a point each second (Hz)

PERIOD = time in seconds for one wave to pass a point (s)

WAVESPEED = speed at which the waves moves through the medium

V = F X (LAMDA)

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## ELECTROMAGNETIC WAVES

electromagnetic waves are trasverse (travel through a vacuum not a medium)

all waves travel at same speed through vacuum (3 x 10^8 m/s)

RED = LOWER FREQUENCY + LONG WAVELENGTH

VIOLET = HIGHER FREQUENCY + SHORT WAVELENGTH

radio --- micro --- infrared --- visible light --- ultraviolet --- x rays --- gamma rays

when electromagnetic waves are genrated or absorbed, changes take place in atoms or nuclei

absorbtion of waves can change energy levels, waves can be emitted and absorbed over a wide frequency range

ultraviolet = skin cancer, x-rays and gamma = ionising radiation, mutation of genes (cancer)

radio waves produced when electrons oscillate in electrical circuits, absorbed by aerials but then the electrons in aerial osicillate, creates alternating current with same frequency of RW

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## REFRACTION

Waves can change direction when they change speed, moving from one medium to another

light to glass = slows down = bend towards the 'normal'

glass to air = speeds up (velocity) = bend away from the 'normal'

wavefront is an imaginary line that connects all the same points in a set of waves

when passing into glass the front of the wavefront slow down, get closer together = smaller wavelength = change direction to normal

when passing into glass AT NORMAL the whole wavefront slows down, no change in direction

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## uses of em waves

RADIO - transmitt radio + terrestrial tv signals (freeview), used because they can trvel long distances before being absorbed, long wavelengths can also spread out between hills, reflect off a layer of charged particles in atmosphere allows us to send radio waves around Earth

MICRO - microwaves oven. communicate with satellites, pass through atmpsohere without being reflected or refracted

INFRARED - cook food in ovens because energy is easily absorbed, heat loss

VISIBLE LIGHT - fibre optics, transmit pulses of light which carry information, telephone and cable TV signals, short wavelength = lots of informations

ULTAVIOLET - energy efficent lightbulbs, contians more energy than viisble light, sun tanning

X RAYS - broken bones,very penetrative, pass through body tissue, absorbed by bones,medical treatment

GAMMA - detect cancers,very penetrative, pass through body tissue, medical treatment

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## FORCES

Momentum (kg m/s) = mass x velocity

closed system = before momentum = after momentum

double velocity of a car = kinetic energy quadruples

BRAKING = friction between brake and wheel, themal energy in brakes, temp increases, a large braking force causes overheat and driver loose control

force = mass x acceleration (newtons 2nd law)

stopping distance = thinking distance + braking distance

thinking distance = distance travelled by the car during the driver's reaction time

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## force2

1ST = stationary resultant force is 0 then it will be stationary, resultant force on moving object is 0 then object will continue moving with same velocity

2ND = acceleration is proportional to the resultant force and inversely proportional to the mass

inertia mass = a measure of how difficult it is to change the velocity of an object, ratio of the force needed to accelerate and object over the acceleration produced

3RD = whenever two objects interact the forces they exert on each other are equal and opposite

acceleration = change in velocity / time

total area under velocity time graph tell us the displacement

terminal velocity = maximum speed of an object, reached when the forces moving the object are balanced by its fricitonal forces (constant velocity)

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