P1 Ch5_1

P1 Ch5_1

1. The Nature Of Waves

   • We use waves to transfer energy and transfer information
   • Transverse waves vibrate at right angles to the direction of energy transfer of the waves. All electromagnetic waves are transverse waves.
   • Longitudinal waves vibrate parallel tot the direction of energy transfer of the waves. A sound wave is an example of a longitudinal wave.
   • Mechanical waves, which need a medium to travel through, may be transverse or longitudinal waves.

2. Measuring Waves

   • For any wave, its amplitude is the height of the wave crest or depth of the wave trough from its position at rest.
   • For any wave its frequency is the number of wave crests pass a point in one second.
   • For any wave, its wavelength is the distance from on wave crest to the next wave crest. This is the same as the distance from one wave trough to the next wave trough.
   • Speed = Frequency x Wavelength

3. Wave Properties : Reflection

   • The normal at a point drawn on a mirror is a line drawn perpendicular to the mirror.
   • For a light ray reflected by a plane mirror...
     • 1. The angle of incidence is the angle between the incident ray and the normal.
       • 2. The angle of reflection is the angle between the reflected ray and the normal.
   • The law of reflection states that:
     • The angle of incidence = the angle of reflection

4. Wave Properties : Refraction

   • Refraction is the change of direction of waves when they travel across a boundary
   • When a light ray refracts as it travels from air into glass, the angle of refraction is less than the angle of incidence
   • When a light ray refracts as it travels from glass into air, the angle of refraction is more than the angle of incidence.

5. Wave Properties : Diffraction

   • Diffraction is the spreading out of waves when they pass through a gap or around the edge of an obstacle
   • The narrower a gap is, the greater the diffraction is.
   • If radio waves do not diffract enough when they go over hills, radio and TV reception will be poor.

6. Sound

   • The frequency range of the normal human ear is from about 20Hz to about 20,000Hz
   • Sound waves are vibrations that travel through a medium. They cannot travel through a vacuum.
   • Echoes are due to sound waves reflected from a smooth, hard surface.
   • Musical Sounds
     • The pitch of a note increases if the frequency of the sound waves increases
     • The loudness of a note increases if the amplitude of the sound waves increases.
     • Vibrations created in an instrument when it is played produce sound waves.