Properties of Waves

Frequency, wavelength, amplitude and time period are used to describe waves.

Waves can be transverse or longitudinal.

Transverse waves - the vibration is at right angles to the wave motion, e.g. light, water waves and the

electromagnetic spectrum waves.

Longitudinal waves - the vibration is parallel to the wave motion, e.g. sound and some earthquake waves.

Wave Speed (m/s) = Frequency (Hz) x wavelength (m)

Reflection is the bouncing of waves off a surface. There are three rules of reflection that you need to know.

1. The angle of incidence always equals the angle or reflection.

2. The distance from the object to mirror is the same as the distance from the mirror to the image.

3. The image is always the same size as the object but is laterally inverted.

Refraction is the bending of a wave when it goes from one substance into another. Refraction happens because

the speed and wavelength of the wave changes as the wave goes into the other substance. The frequency of the

wave stays the same.

Total internal reflection happens when the angle of incidence, of a wave going from a substance into air, is

greater than the critical angle. The wave bounces off the boundary, obeying the rules of reflection.

Dispersion of white light produces a spectrum. This is caused by refraction. Light of different frequencies is

refracted by different amounts. Red is refracted the least and violet the most. This causes white light to be split

up into separate colours.

Diffraction is the spreading out of a wave as it goes through a gap, or around an object. The smaller the gap or

the larger the wavelength the greater the diffraction.

Diffraction is most effective when the size of the gap is approximately the same as the wavelength of the wave.

You will need to be able to draw diagrams showing how waves reflect, refract and diffract.

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Uses of Waves

Sound waves are caused by particles vibrating. The frequency of the vibration decides the pitch of the sound.

The amplitude of the vibrations decides the loudness of the sound.

Ultrasound waves are high frequency sound waves, which are beyond the human hearing range. Ultrasound is

used for seeing babies in the womb, detecting cracks in metal and cleaning instruments.

Waves can be represented on an oscilloscope screen, which can be used to measure the characteristics of the

waves. You should be able to find the amplitude and time period of a wave from an oscilloscope screen.

The electromagnetic spectrum is a series of waves that all travel at the same speed in a vacuum. They are

all transverse. Each part of the spectrum has different uses and dangers. Each part of the spectrum has a

different frequency and wavelength. Gamma waves are at the high frequency end of the spectrum. Radio waves

are at the low frequency end. You will need to know the uses and dangers of each part of the spectrum.

Different surfaces and materials absorb different frequencies of waves. White surfaces reflect most waves. Black

surfaces absorb most waves.

Information can be carried along copper cables as electrical signals, or along optical fibres as electromagnetic

wave pulses.

Optical fibres have advantages over copper cables. Optical fibres can carry more information; the signals can

travel faster and lose less energy as they travel along the cable.

There are two types of signals, analogue and digital. Analogue signals have a continuous range of

values. Digital signals have only two values, on (1) and off (0).

Digital signals have advantages over analogue signals. Digital signals are easier to transmit as they are less

affected by noise; it is also possible to send more information, in a certain time, as a digital signal than as an

analogue signal.