Reflection, refraction and diffraction of waves
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 1 worked example, 6 practice questions, 2 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- Three things waves do
- The ripple tank
- Reflection
- The law of reflection
Read the transcript of the teaching part
Last time
Before we start: last time, in Conduction, convection and radiation, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
Three things waves do
Shout at a cliff, and you hear an echo. Walk behind a wall, and you can still hear a friend on the other side. Put a spoon in water, and it looks bent. These are three different things that waves do. They are reflection, refraction and diffraction, and each one has a clear rule.
The ripple tank
To study water waves we use a ripple tank: a shallow tray of water with a vibrating bar that makes straight waves. A lamp above shines through the water onto a screen, and the crests show as bright lines. A line along the top of a crest is called a wavefront. The waves travel at right angles to the wavefronts.
Reflection
Reflection is when a wave hits a barrier and bounces back, staying in the same medium. The normal is a line drawn at right angles to the surface, at the point where the wave hits. The law of reflection says that the angle of incidence equals the angle of reflection. Both angles are measured from the normal. The speed, frequency and wavelength of the wave do not change.
The law of reflection
A ray comes in and hits the mirror. The dashed line at right angles to the mirror is the normal. The ray leaves at the same angle on the other side of the normal. Always measure both angles from the normal, and not from the surface.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Reflection, refraction and diffraction of waves.
The whole chapter: General Properties of Waves, General Properties of Waves.
Chapter 3.1: General properties of waves
- Transverse and longitudinal waves, and wave speed 6 min
- Reflection, refraction and diffraction of waves 6 min
Also for O Level Physics 5054
Which topics come up most in O Level Physics 5054 past papers, counted from every paper since 2004.