Waves
Vocabulary Review
Properties of Waves
The Electromagnetic Spectrum
Vocabulary Review
• Progressive waves
• Describing wave motion
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Displacement
Amplitude
Wavelength
Period
Frequency
Speed
Intensity
• Energy passing through a unit area in unit
time.
• Intensity ~ Square of the amplitude
• I ~ A2
• Intensity ~ 1/d2
• Where d is distance from source
Example 1
• A health inspector is measuring the
intensity of a sound. Near a loudspeaker
his meter records an intensity I. This
corresponds to an amplitude A of the
sound wave. At another position the
meter gives an intensity reading of 2 I.
What is the corresponding sound wave
amplitude?
Example 2
• The intensity I of a sound at a point P is
inversely proportional to the square of
the distance x of P from the source of the
sound. Air molecules at P, a distance r
from S, oscillate with amplitude 8.0 μm.
Point Q is situated a distance 2r from S.
What is the amplitude of oscillation of
air molecules at Q?
Phase
• The angle at which the wave motion
started.
Phase
0⁰
180⁰ or п
Phase
90⁰ or п/2
270⁰ or 3п/2
Phase Difference
• The difference in angles between two
waves at a specific point.
Phase Difference
Phase difference
of п at all points
Phase Difference
Phase difference
of п at all points
Coherence
When two waves have constant phase
difference, then they are coherent.
Coherence occurs when two waves have
the same frequency or period.
Non-Coherence
In Phase
Phase difference
is a multiple of 2п
at all points.
Out of Phase
Phase difference
is not a multiple
of 2п.
Out of Phase
Phase difference
of п at all points
Wave Properties
• For all waves
– Reflection
• Bouncing of waves off a surface
– Refraction
• Change of wave speed as it passes from one medium
to another (from one depth to another)
• Bending of waves
– Diffraction
• Bending of waves around a barrier
Wave Properties Question
• Which wave properties change when
light passes from air into glass?
• A colour and speed
• B frequency and wavelength
• C speed and wavelength
• D wavelength and colour
Polarisation
• Oscillation that takes place in one
direction.
• Only true for transverse waves.
Polarisation
The Electromagnetic
Spectrum
• Electromagnetic waves are transverse
waves
• They are non-mechanical waves
– Do not require a medium to transfer energy
• Travel at the same speed in a vacuum
– 3 x 10 8 ms-1
Orders of Magnitude
(Wavelength)
• Gamma Rays
• X-Rays
• Ultraviolet Rays
• Visible Light
– ROY G BIV
• 10 -14 m
• 10-10 m
• 10-7 m
• 10-7m
• (700 nm -400 nm)
Orders of Magnitude
(Wavelength)
• Infrared
• Microwaves
• Radio Waves
• 10 -6 m
• 10-2 m
• 10 2 m