Waves, Light and Sound for Singapore N(A)-Level Science (Physics) 5105/5106: general wave properties and the wave equation, the reflection and refraction of light, and sound as a longitudinal wave with pitch, loudness and echoes

What this module covers

Waves, Light and Sound studies how energy travels as a wave in N(A)-Level Science (Physics) 5105/5106. It first sets out the language common to all waves, wavelength, frequency, amplitude and speed, tied together by the wave equation. It then looks at light, how it reflects off surfaces and refracts at boundaries, and at sound, a wave you can hear, explaining why some sounds are high and some are loud.

Waves carry energy without carrying matter, an idea that runs from ripples on water to the light from a screen and the sound of a voice. Each dot point below has full worked answers and practice questions.

General wave properties

General wave properties defines the quantities shared by all waves. Wavelength is the distance between corresponding points, frequency is the number of waves per second in hertz, amplitude is the greatest displacement from rest, and speed is how fast the wave moves. They are linked by the wave equation:

Reflection and refraction of light

Reflection and refraction of light describes what light does at surfaces and boundaries. The law of reflection states that the angle of incidence equals the angle of reflection, both measured from the normal. Refraction is the bending of light as it changes speed crossing into a new transparent medium: it bends towards the normal entering a denser medium and away from the normal on leaving.

Sound waves

Sound waves explains sound as a longitudinal wave, where air particles vibrate back and forth along the direction of travel, forming compressions and rarefactions. The pitch depends on frequency (higher frequency, higher pitch) and the loudness depends on amplitude (larger amplitude, louder sound). Sound needs a medium and cannot travel through a vacuum. Echoes use reflection, and the distance to a reflector follows

How this module is examined

• Apply $v = f\lambda$. Convert units first, then rearrange for the quantity asked.
• Measure angles from the normal. Both the angle of incidence and the angle of reflection are measured from the normal, not the surface.
• Link pitch and loudness. Pitch follows frequency; loudness follows amplitude; sound needs a medium.

Check your knowledge

Recall and calculation questions across the module. Attempt them, then check the worked solutions.

1. Define the amplitude of a wave. (1 mark)
2. A wave has frequency $50\ \text{Hz}$ and wavelength $4.0\ \text{m}$. Calculate its speed. (2 marks)
3. State the law of reflection. (2 marks)
4. Explain why sound cannot travel through a vacuum. (2 marks)
5. State what happens to the pitch of a sound if its frequency increases. (1 mark)