Waves - Light and Sound

Properties of waves

longitudinal waves à move in the same direction as the medium movement

transverse waves à move at right angles to the medium movement

amplitudeà hight from top to bottom, unit: metre (m)

frequency how many pass each second, unit: hertz (Hz)

wavelength  length from start to end of wave, unit: metre (m)

period  time taken for wave to pass = 1/frequency

	waves transfer energy and information without transferring matter wave speed = frequency × wavelength v = f × λ frequency = 1/ time period f = 1/ T waves can be diffracted (spread out) through gaps or when they pass an edge, and the extent of diffraction depends on the wavelength and the physical dimension of the gap
Christian Doppler (Discovered the doppler effect)

The electromagnetic spectrum

electromagnetic spectrum goes from longest wavelength -- radio, microwave, infra-red, visible, ultraviolet, X-ray and gamma rays – shortest wavelength

electromagnetic waves travel at the same speed in free space

uses of electromagnetic radiations,

• radio waves: broadcasting and communications

• microwaves: cooking and satellite transmissions

• infra-red: heaters and night vision equipment

• visible light: optical fibres and photography

• ultraviolet: fluorescent lamps

• X-rays: observing the internal structure of objects and materials and medical applications

• gamma rays: sterilising food and medical equipment

Detrimental effects of excessive exposure of the human body to electromagnetic waves

• microwaves : internal heating of body tissue

• infra-red : skin burns

• ultraviolet : damage to surface cells and blindness

• gamma rays : cancer, mutation

Light

light waves are transverse waves which can be reflected, refracted and diffracted

the angle of incidence equals the angle of reflection

refractive index   n=sin i/sin r

total internal reflection is used in transmitting information along optical fibres

when the angle of incidence is greater than the critical angle c there is total internal reflection

the relationship between critical angle c and refractive index N is  sin c = 1/N

sound

sound waves are longitudinal waves which can be reflected, refracted and diffracted

the frequency range for human hearing is 20 Hz – 20 000 Hz

an oscilloscope and microphone can be used to display a sound wave by converting it to an electrical signal

the pitch of a sound depends on the frequency of vibration

the loudness of a sound depends on the amplitude of vibration