Vocabulary Review Properties 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 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 Refraction Diffraction 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