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CHAPTER TWELVE: WAVES
Waves & Vibrations

WAVE is any oscillation where energy is transferred in the direction of the wave travel
without the large scale/long distance permanent displacement of matter.

MECHANICAL WAVES ELECTROMAGNETIC WAVES

When waves progress through a substance, the EM waves are vibrating electric and magnetic fields
particles…

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Transverse Wave: DisplacementDistance Graph




Key Terms:
Displacement: distance and direction from the equilibrium point
Amplitude: maximum displacement from equilibrium
Wavelength: distance between 2 adjacent particles which have the same phase
Frequency: number of oscillations per second by the source / number of waves passing a point
per second. Unit =…

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Phase Difference:

PHASE DIFFERENCE between two vibrating particles is the fraction of a cycle between
the vibrations of the two particles.



Phase Difference is measured either in degrees or radians, where

1 cycle = 360° = 2 radians

For two points at distance (d) apart along a wave of wavelength…

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DisplacementDistance graphs:
A displacementdistance graph is also called a displacementposition graph. It shows
the displacement of the particles at various positions at a certain time.
Although it looks like a photograph of a transverse wave, it can be used to describe
BOTH a transverse and a longitudinal wave (Figures a.…

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Fig c. Time series of DisplacementDistance graphs of a wave.



Using a series of displacementdistance graphs at various times, we can see the
motion of the wave (Figure c.)
By comparing the changes in these graphs, we can deduce the travelling speed and
direction of the wave, as well as…

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Period (and hence, the frequency)
Direction of motion of the particle at various times

If we have a snapshot of the wave too, we can deduce the motion of the wave (i.e. its
travelling speed and direction)




Polarisation

POLARISATION is the restriction of transverse waves using a filter (mechanical/
electronic)…

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Unpolarised Polarised

Plane of Polarisation: The plane in which the medium oscillates and the energy is
propagated. (For Electromagnetic waves it is defined as the plane in which the electric field
oscillates)

Polarisation can be used to distinguish between longitudinal and transverse waves since only
transverse waves show polarisation effects.…

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AXES PARALLEL
The light from the Polaroid is plane polarised, so the transmitted intensity will be a
maximum when the analyser is parallel to the plane of polarisation.




AXES PERPENDICULAR
Intensity will be zero when analyser is at right angles to polariser.

In a 360° rotation of the analyser the…

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Applications
Polaroid Sunglasses: Only let light polarised in one direction and absorb the rest.
Intensity is reduced. Also, reflected light and sunlight scattered from particles in the
atmosphere is partially polarised. If the Polaroid in the sunglasses is in the correct
orientation it can absorb the reflected light and greatly…

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REFRACTION is the change of direction of a wave when it crosses a boundary
where its speed changes.
This change in velocity means that the wavelength of the wave must change, since
frequency is constant and v = f

Diffraction
DIFFRACTION is the spreading of waves on passing through a…

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Rachael

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thanks

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