1.5- Features of Waves

1.5- Features of Waves

1. Transverse and Longitudinal Waves

   • There are two different types of waves: transverse and longitudinal. Transverse are when the direction of motion is at right angles to the direction of vibration. Longitudinal waves are when the direction of motion is the same as the direction of vibration. Transverse waves travel in a series of troughs and peaks, longitudinal waves travel as compressions and rarefractions.

2. How do we describe waves?

   • Waves are described in terms of their wavelength, frequency, speed and amplitude. The diagram below shows this on a transverse wave.
     • Wavelength is the distance the wave takes to repeat itself- normally measured form crest to crest. Wavelength is measured in metres.
     • Frequency is the number of waves that pass a point in 1 second. Frequency is measured in hertz, Hz, where 1Hz = 1 wave per second
     • Speed of a wave is the distance that a wave travels in 1 second. Wave speed is measured in metres per second, m/s
     • Amplitude of a wave is the measure of the energy carried by the wave. amplitude is measured from the undisturbed/normal position to the top os a crest or bottom of a trough.

3. Calculating wave speed, frequency and wavelength

   • Wave speed can be calculated using the equation:
   • Wave speed, frequency and wavelength can be calculated using:
   • Waves all travel at different speeds
   • all electromagnetic waves travel at the speed of light (3xten8)

4. Electromagnetic Spectrum:

   • The electromagnetic spectrum is a family of transverse waves that all travel at the same speed in a vacuum, 300000000 m/s. Like the energy given out by radioactive materials, electromagnetic waves are also called radiation.
   • Different parts of the electromagnetic spectrum have different wavelengths, frequencies and energies. the higher the frequency, the higher the energy. The three things determine the wave's properties and how it will behave.
   • Gamma rays- have very high energy and can ionise (kill or damage) cancer cells, but they are also used to make images of the body.
   • X-rays: are also ionising and are used in medical equipment.
   • Ultraviolet light: can ionise skin cells which causes sunburn.
   • Ionising radiations: able to react with atoms and damage cells due to their large energies.
   • Infrared radiation: used for heating and communications, such as TV remotes and optical fibres.
   • Microwaves: used for heating and communicating, particularly mobile phone signals.
   • Radio waves- communications over long distances, transmitting TV and radio programmes.

5. Reflection of Waves

   • Reflection is a fundamental property of all waves. when straight (plane) wave-fronts hit a flatt barrier, they rebound off, obeying the law of reflection
   • The imaginary rays, drawn at right-angles to the wave-fronts, show the direction of travel of the wave-fronts. the angles between the incident and reflected rays and the normal line are equal, obeying the law of reflection where:
     • angle of incidence = angle of reflection
   • The normal is a line drawn at 90 degrees to a surface where waves are incident.
   • The angle of incidence is the angle between the incident ray and the normal.
   • The angle of reflection is the angle between the reflected ray and the normal.

6. Refraction of Waves:

   • when water waves travel from deep water into shallow water, they slow down and the wave-fronts get closer together, decreasing their wavelength. This effect is called refraction. When the wave-fronts hit the boundary between the deeper water and the shallow water at an angle, they appear to change direction.
   • The refraction of light through a glass block shows the rays of light changing direction as they go from the air into the glass, and then back again.

7. Communicating Using Satellites

   • Mobile phones use microwaves and, as they are wireless signals, you don't need a copper cable or optical fibre. However, one disadvantage of using microwaves is that there must be a clear path between transmitter and receiver. To cover the largest area, transmitters are placed in hills. The curvature of the Earth means that repeater stations have to relay the microwave signal to distant transmitters. satellites are used for long distant communications around the world. Theoretically, only three would be needed, but more are used. Satellites are placed in orbit at 36000km. They orbit the e=Earh above the equator, in time with the Earth's rotation. This is called geostationary/geosynchronous orbit.

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