waves vocabulary review properties of waves the electromagnetic spectrum
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Waves
Vocabulary ReviewProperties of Waves
The Electromagnetic Spectrum
Vocabulary Review• Progressive waves• Describing wave motion
– 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 corresponding angular displacement relative to a complete wave of a point on the wave
Phase
180⁰ or п
0⁰
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
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