AS Physics Waves OCR Notes

AS Physics Waves OCR Notes

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Module 4: Waves
Spread 1: Wave Motion:
Key Definitions:
Progressive Wave: Waves that travel away from a source.
Transverse Wave: A wave where oscillations of particles are perpendicular to the direction of
the wave's motion. For example, water waves and EM waves.
Longitudinal Wave: A wave where oscillations of particles are parallel to the direction of the
wave's motion. For example, sound waves.
You can see that particle A is moving upwards, while particle B is moving downwards to create
the wave movement. All the particles oscillate vertically but do not move forwards or backwards, even
though the wave moves forward.

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Sound waves are pressure waves (caused by the vibrations of particles). In one region, some particles
are moving towards each other (compressions: areas of high pressure ) and other particles are moving away
from each other (rarefactions: areas of low pressure).…read more

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Wavelength: The smallest distance between one point on a wave and the identical point on
the next wave (e.g. the distance from one peak to the next peak), measure in metres.
Period: The time taken for one complete pattern of oscillation, measure in seconds.
Frequency: Number of oscillations per unit of time, measure in hertz. Calculated by using
1/period.
Displacement: The distance that any part of a wave has moved from its rest position. Can be
positive or negative.
Amplitude: The maximum displacement, e.g.…read more

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Deriving the Formula:
· Speed = Distance/Time
· Therefore, wave speed = Wavelength / (1/f)
· Wave speed = Frequency x Wavelength.
How a Progressive Wave Transfers Energy:
· In the case of light, energy is transferred from a source to your eye. The wave transfers
photons to your eye.
· In the case of sound, energy is transferred from a source to your ear. The wave causes
particles in air to vibrate and collide with other particles to transfer the energy.…read more

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Refraction: When waves change direction when they travel form one medium to another, due
to a difference in wave speed in each medium.
Diffraction: When waves spread out after passing around an obstacle or through a gap.
Reflection:
· One of the most common phenomena that we see is reflection. When a wave is reflected
from a surface, the angle of incidence will be equal to the angle of reflection. The wavelength of a
wave does not change after it has been reflected.…read more

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This phenomena describes the change in direction of motion, as a wave enter one medium
from another. The change in direction is due to the change in speed of the wave. As light passes from
a less dense material to a more dense material, the speed of the wave decrease.
· When a wave enters a denser medium, it bends towards the normal. The speed of the wave
decreases and the wavelength decreases therefore.…read more

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Gamma Rays 10-16 10-9 3 x1024 3 x1017 Nuclear Decay Photographic Diagnosis and
film/Geiger cancer
tube treatment
X-rays 10-12 10-7 3 x1020 3 x1015 Bombarding Photographic X-ray
metals with film photography/Cr
high energy ystal structure
electrons analysis
Ultraviolet 10-9 3.7 x10-7 3 x1017 8 x1014 High Photographic Disco
temperature film/Sunburn lights/Tanning
solids and Studios
gases
Visible Light 3.7 x10-7 7.4 8 x1014 4 x1014 High Retina of eye Sight/
x10-7 temperature Communication
solids and
gases
Infrared 7.…read more

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Telecommuni
electric fields circuits cations
in aerials
Ultraviolet:
· UV-A: Wavelength 315-400nm
Causes tanning when skin is exposed to the sun (accounts for 99% of UV).
· UV-B: Wavelength 280-315nm
Causes damage such as sunburn and skin cancer.
· UV-C: Wavelength 100-280nm
Filtered out by the atmosphere and does not reach the surface of the Earth.
Spread 6: Polarisation:
Key Definitions:
Polarisation: The process of turning an unpolarised wave into a plane-polarised wave.
Plane-polarised wave: A transverse wave oscillating in one plane only.…read more

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Transverse waves have oscillations perpendicular to the wave's direction of travel. The
oscillations of the particles can be in any direction, as long as they are at right angles to the wave's
motion.
Polarising filters called 'Polaroids' cause oscillations to occur in one plane only; this is called a
plane-polarised wave.
Longitudinal waves cannot be polarised, as they do not have oscillations perpendicular to the
wave's direction of travel. For a wave to be polarised, it must be a transverse wave.…read more

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A normal light wave passes through a sheet of polaroid. The first polaroid sheet is called a
polariser. It produces plane-polarised light. The light wave then carries on to a second sheet of
polariod, called the analyser, which is rotated through an angle X, relative to the polariser sheet. The
plane of polarisation will be rotated by an angle X. Since the intensity is proportional to amplitude
squared, the intensity of the wave is reduced after it passes the second filter.…read more

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