Longitudinal waves: the vibrations are parallel to the direction of the wave (sound) e.g. | | | ||| ||| | | ||
Transverse waves: the vibrations are perpendicular to the direction of the wave (water, EM waves)
Wavelength: the distance from a point on one wave to the equivalent point on the adjacent wave.
Amplitude: the maximum displacement of a point on a wave away from its undisturbed position (high amplitude = high volume).
Frequency: the number of waves passing a point each second (high frequency = high pitch).
Period: the time taken for one wave to pass a point.
T = 1/f
v = fλ
T: time period (s), f: frequency (Hz), v: speed (m/s), λ: wavelength (m)
Electromagnetic waves are always transverse, travel at the same velocity through a vacuum.
HIGHEST WAVELENGTH, LOWEST FREQUENCY
Uses: RADIO: tv and radio, MICROWAVES: satellite communications, cooking food, INFRARED: electrical heaters, cooking food, infrared cameras, VISIBLELIGHT: fibre optic communications, ULTRAVIOLET: energy efficient lamps, sun tanning, X-RAYS and GAMMA: medical imaging and treatments.
LOWEST WAVELENGTH, HIGHEST FREQUENCY
Radio waves can be produced by oscillations in electrical circuits.
When they are absorbed they may create an alternating current with the same frequency, so radio waves can themselves induce oscillations in an electrical circuit.
Different substances may absorb, transmit, refract or reflect electromagnetic waves.
Refraction: when waves change direction as they enter a new medium. For example, when light enters glass from air, it slows down, so it bends (towards the normal).
Diagrams: the normal is perpendicular (90 degrees) to the boundary. If the ray slows down, it bends towards the normal. If it speeds up, it bends away from the normal.
Reflection: when a wave bounces back off a surface.
Angle of incidence = angle of reflection (measure both using the normal).
Sound waves can travel through solids causing vibrations.
In the ear, sound waves cause the ear drum to vibrate which causes sound.
Human ear:
Outer ear collects sound as a pressure air wave. Sound hits the eardrum (tightly stretched membrane which vibrates at the same frequency as the sound wave).
Vibrations transmitted to fluid in innear ear (cochlea).
Small hairs with nerve cells also move, electrical impulse released.
The frequency range of human hearing is 20-20,000 Hz.
Ultrasound waves have a frequency above 20,000 Hz.
Ultrasound waves are partially reflected when they meet a boundary between two media. The time taken for the reflections to reach a detector can be used to determine how far away such a boundary is. This allows ultrasound waves to be used for both medical and industrial imaging.
Ultrasound: sound with frequencies above 20,000 Hz.
Sonar (detect seabed): send pulse of ultrasound below a ship. Count time taken and half it to calculate depth.
Foetalscanning: not harmful. creates image of foetus. ultrasoudn waves partially reflect at each boundary, so distances can be worked out.
Infrasound: frequency below 20 Hz.
p-waves: longitudinal, pass through solids and liquids.