Waves Vocabulary Review Properties of Waves The Electromagnetic

Waves 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 ~ A 2 • Intensity ~ 1/d 2 • 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 2 r 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 3 п/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 difference is a multiple of 2 п at all points.

Out of Phase difference is not a multiple of 2 п.

Out of 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 • (700 nm -400 nm)

Orders of Magnitude (Wavelength) • Infrared • Microwaves • Radio Waves • 10 -6 m • 10 -2 m • 10 2 m