Waves

Waves

1. The Nature of Waves

   • We use waves to transfer energy and information.The direction of trevel of the wave is the direction in which the wave transfers energy
   • There are different types of wave
     • For a transverse wave the oscillation (vibration) of the particles is perpendicular (art right angles) to the direction in which the wave travels
     • For a longitudinal wave the oscillation of the particles is parallel to the directon of travel of the wave
       • A longitudinal wave is made up of compressions and rarefractions
   • Electromagnetic Waves
     • Light waves and radio waves can travel through a vacuum. There are no particles moving in an electromagnetic wave, as these waves are oscillations in electric and magnetic fields. The oscillations are perpendicular to the direction of travel of the wave. so all electromagnetic waves are transverse waves.
   • Mechanical waves
     • Waves on springs, and sound waves, travel through a medium (substace. Mechanical waves may be transverse or longitudinal.
       • Sound waves are longitudinal waves
   • Key Words
     • Transverse wave
     • Oscillation
     • Perpendicular
     • Longitudinal wave
     • Compression
     • Rarefraction
     • Electromagnetic wave
     • Mechanical wave

2. Measuring Waves

   • The AMPLITUDE of a wave is the height of the wave crest or the depth of the wave trough from the position at rest.
     • The greater the amplitude of a wave the more energy it carries
   • The WAVELENGTH of a wave is the distance from one crest to the next crest, or from one trough to the next trough
   • The FREQUENCY of a wave is the number of wave crests passing a point in one second . The unit of frequency is the hertz (Hz). This unit is equivalent to per second (s).
   • The speed of a wave is given by the equation: s = f x w
     • Where:
       • s is the wave speed in meters per second, m/s
       • f is the frequency in hertz, Hz
       • w is the wavelength in meters, m
   • The diagram shows a transverse waver, but the same terms apply to a longitudinal wave
   • The wavelength of a longitudinal wave is the distence from the middle of one compression to the middle of the next compression. This is the same as the middle of one rarefraction to thew middle of the next rarefraction
   • The frequency of a longitudinal wave is the number of compressions passing a point in one second
   • Key Words
     • Amplitude
     • Wavelength
     • Frequency
     • Speed

3. Wave Properties

   • Reflection
     • The Law of Reflection
       • The image shown in a mirror is due to the reflection of light.
       • The diagram shows how an image is formed by a plane (flat) mirror. The incident ray is the ray that goes towards the mirror. the reflected ray is the one coming away from the mirror
       • We draw a line called the normal, perpendicular to the mirror at the point where thew incident ray hits the mirror.
       • 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.
       • For any reflected ray the angle of incidence is equal to the angle of reflection.
     • Image formation by a plane mirror
       • The image in the plane mirror is
         • the same size as the object
         • upright
         • the same distance behind the mirror as the object itself
         • virtual
       • A real image is one that can be formed on ascreen, because the rays of light that produce the image actually pass through it.
       • A virtual image cannot be formed on a screen, because the rays of light that produce the image only appear to pass through it
     • Key Words
       • Plane mirror
       • Normal
       • Angle of incidence
       • Angle of reflection
       • Real image
       • Virtual image
     • Grade booster
       • Make sure that you understand the difference between a real image and a virtual image.
   • Refraction
     • Waves change speed when they cross a boundary between different substances. The wavelength of the wave also changes, but the frequency stays the same.
     • Refraction is a property of all waves, including light and sound. For example, a light ray refracts when it crosses a boundary between two substances such as air and glass, or air and water.
     • The change in speed of the waves causes a change in direction.
     • When light enters a more dense substance, such as going from glass, it slows down and the ray changes direction towards the normal.
     • When light enters a less dense substance, such as going from glass to air, it speeds up and the ray changes direction away from the normal.
     • Different colours of light have diifferent wavelengths, and are refracted by slightly different amounts. When a ray of light is shone onto a triangular glass prism we can see this because a spectrum is produced. This is called dispersion.
       • Violet light is refracted the most.
       • Red light is refracted the least
   • Difrraction
     • Diffraction is a property of all waves, including light and sound. It is the spreading of waves when they pass through a gap or round an obstacle.
     • The effect is most noticeable if the wavelength of the waves is about the same size as the gap or the obstacle.
     • 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.
     • Key Words
       • Diffraction
     • Grade Booster
       • If you are drawing a diagram to show Diffraction, make sure that the wavelength of the waves stays the same.

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