Waves P12-15

Waves P12-15

1. Reflection and refraction

   • Reflection of waves can be investigated using ripple tanks. Each ripple is called a wavefront.
   • Refraction of waves is the change of the direction in which they are travelling when they cross a boundary between one medium and another medium.
   • Materials and waves
     • When a wave is directed at a substance, some or all of the wave may be reflected at the surface.
       • What happens is dependent on the wavelength of the wave and also on the substance (eg. microwaves are reflected my metal surfaces but can pass through paper)
     • Of the waves that go into a substance, some or all of them may be absorbed, heating the substance as it would gain energy from the wave (eg. food in a microwave)
     • As waves travel through a substance, the amplitude gradually decreases as the substance absorbs some of it's energy
     • Waves that are not absorbed by the substance they are travelling through are transmitted by it (eg. light is mostly transmitted by ordinary glass, but is almost completely absorbed by darkened glass)

2. Investigating sound waves

   • Sound waves are easy to produce, our vocal cords vibrate and produce sound waves every time we speak.
   • Sound waves cannot travel through a vaccum.
   • Sound waves reflect from smooth, hard surfaces such as bare walls. if you clap your hands in a large bare hall, you will hear the echo a short time later. The time delay is because the waves travel to the wall and back to you before you hear the echo.
   • If the distance to the nearest wall and the time delay are measured, the speed of sound in air can be calculated using the equation:
     • Speed= distance to the wall and back/time delay