WAVES
- 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)
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
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
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
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
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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