Waves: Part 1

Waves: Part 1

1. The Nature of Waves

   • We use waves to transfer energy and information
   • The direction of travel of the wave is the direction in which the wave transfers energy
   • For a transverse wave, the oscillation is perpendicular to the direction at which the wave travels
     • Transverse Waves
   • For a longitudinal wave, the oscillation is parallel to the direction of travel of the wave
     • Longitudinal Waves
   • A longitudinal wave is made up of compressions and rarefactions
   • Electromagnetic waves (e.g. light waves and radio waves) can travel through a vacuum
     • Electromagnetic Waves
   • There are no particles moving in the electromagnet wave, as these waves are oscillations in electric and magnetic fields
   • The oscillations are perpendicular to the direction of travel to the wave - TRANSVERSE
   • Mechanical waves (e.g. waves on springs and sound waves) travel through a medium (substance)
     • Mechanical Waves
   • Mechanical waves can be TRANSVERSE & LONGITUDINAL
   • Sound waves - LONGITUDINAL

2. Measuring Waves

   • AMPLITUDE - height of the wave crest or the wave trough from the position at rest
   • greater amplitude = more energy it travels
   • WAVELENGTH - distance from one crest to the next or from one trough to the next
   • FREQUENCY - number of wave crests passing a point in one second in Hertz (Hz)
   • The wavelength of a longitudinal wave is the distance from the middle of one compression to the middle of the next compression
   • This is the same as the middle of one rarefaction and the next rarefaction
   • The frequency of a longitudinal wave is the number of compressions passing a point per second

3. Wave Properties: Reflection

   • The image seen in a mirror is due to a reflection of light
   • An image is formed by a plane (flat) mirror
   • INCIDENT RAY = ray going towards the mirror
     • REFLECTED RAY = goes away from mirror
   • Angle of Incidence is the angle between the incident ray and the normal line
   • Angle of reflection is the angle between the reflected ray and the normal line
   • The image in a plane mirror is....
     • - the same size as the object
       • - upright
         • - same distance behind the mirror as the object in front
           • - virtual
   • REAL IMAGE = one that can be formed on a screen because the rays of light that produce the image actually pass through it
   • VIRTUAL IMAGE = cannot be formed on a screen, because the rays of light that produce the image only appear to pass through it

4. Wave Properties: Refraction

   • Waves change speed as they cross a boundary between different substances - e.g air & glass
     • the wavelength changes but the frequency stays the same
   • The change in speed of the waves causes a change in direction
   • When light enters a more dense substance (such as going from air to glass) it lows down, and the wave changes direction towards the normal
   • When light enters a less dense substance (such as going from glass to air) it speeds up and the wave changes direction away from the normal
   • However, if the wave is travelling along the normal, it will not be refracted
   • Different colours of light have different wavelengths and are refracted slightly by different amounts
   • When a ray of white light is shone onto a triangular prism, we can see this because a spectrum is produced
   • Violet light - REFRACTED MOST
     • Red light - REFRACTED LEAST

5. Wave Properties: Diffraction

   • Diffraction is a property of all waves (including light and sound)
   • It is the spreading of the waves when they pass through a gap or around obstacles
   • TV signals are carried by radio waves
   • People living in hilly areas may not be able to receive a signal, because it is blocked by a hill
   • Radio waves passing the hill will be diffracted round the hill
   • If they do not diffract enough, the radio and TV signals will be poor