# Sound

Waves, wave motion, sound and light wave nature.

Travelling mechanical wave = Disturbance carrying energy through a medium with no overall media movement

Travelling wave =  weather electromagnetic or mechanical it transfers energy from a source to other areas.

Transverse wave = direction of vibration is perpendicular to the direction in which the wave travels.

Longitudinal wave = direction of vibration is parallel to the direction in which the wave travels.

Frequency is the number of wavelengths that pass a point in one second and the unit is Hertz.

Wave parts = crest, wavelength, node, antinode, amplitude, trough. Draw a wave and place these labels on it

Reflection is the bouncing of waves off an obstacle in their path.

Refraction is the changing of direction of a wave due to a speed change of the wave.

Diffraction = Sideways spreading of waves into an area beyond a gap.

Interference = When two waves meet, the resulting new wave is the algebraic sum of the two original waves.

Constructive interference = When 2 waves meet the resulting new waves amplitude is greater than the algebraic sum of either of the two original waves. Destructive = algebraic sum less than either original wave.

Interference pattern = when two waves meet this is the pattern produced..

Coherent Sources = If two wave are in phase or have a constant phase difference.

Polarisation = this is when a wave is made to vibrate in one direction only. Only transverse waves can be polarised. Light is a transverse wave.

Stationary wave = When two waves with equal frequency and amplitude move in opposite directions they interfere producing a standing wave.

Doppler effect = Apparent change in frequency of a wave due to the motion of a source or observer.

Distance from node to next node is half a wavelength. From node to antinode is quarter wavelength.

Sound displays all of the above characteristics of waves and therefore is a wave. (longitudinal wave).

Overtones = Frequencies which are multiples of certain frequencies. F = frequency, 2f & 3f = overtones.

Harmonics =  Frequencies which are multiples of certain frequencies. F the frequency is 1st harmonic.

Spectrometer: (parts) Base, turntable, collimator, astronomical telescope, eyepiece, Vernier scale.

(Setup): focus cross hairs, focus telescope on distant object, adjust slit width, ensure turntable is level.

Diffraction Grating: A transparent material containing opaque lines that are very close together.

Grating Constant:  This is the width of one line and one slit on a diffraction grating.

Calculating Grating constant: 600 lines per mm = 1/600,000 = 1,666X10-6m .

Dispersion: The breaking up of white light into its different colours or wavelengths. Can be done using prism.

Recombination: The bringing together of the wavelengths (colours) that make up white light. Use two prisms

Primary Colours = Red, Green Blue. Secondary Colours = Yellow, Cyan Magenta.

Complementary Colours = A mixture of a primary and secondary colour that results in white.

Electromagnetic Spectrum: Gamma, X and UV rays. Visible light, infrared, microwaves and radio waves.

Greenhouse effect: heating of earth due to heat being trapped in the atmosphere by insulating gases.