Wave Model

Introduction

The wave model explains how energy travels through space or through a medium without a net transport of matter. The guide asks students to compare transverse, longitudinal, mechanical, and electromagnetic waves using the same core language of wavelength, frequency, period, and speed.

Guide Focus

• Describe transverse and longitudinal travelling waves.
• Use v = f lambda = lambda / T.
• Compare sound, mechanical waves, and electromagnetic waves.

Key Concepts

1. Travelling waves

A travelling wave is a moving disturbance. Transverse waves have oscillations perpendicular to the direction of energy transfer, while longitudinal waves have oscillations parallel to it.

2. Wave quantities

Wavelength lambda is the distance between equivalent points on adjacent cycles. Frequency f is cycles per second, period T is time per cycle, and wave speed is v = f lambda = lambda / T.

3. Sound waves

Sound is a mechanical longitudinal wave. It requires a medium and travels through compressions and rarefactions of particles.

4. Electromagnetic waves

Electromagnetic waves are transverse oscillations of electric and magnetic fields. They can travel through vacuum and include radio, microwave, infrared, visible, ultraviolet, X-rays, and gamma rays.

Common Mistakes

• Saying particles travel with the wave from source to detector.
• Confusing wave speed with particle oscillation speed.
• Assuming all transverse waves are electromagnetic.

Exam Tips

• When frequency changes but medium stays the same, wave speed usually stays fixed and wavelength changes.
• Use diagrams to show particle displacement separately from wave direction.
• For electromagnetic spectrum questions, remember that higher frequency means shorter wavelength.

Practice Questions

Question 1 (Multiple Choice)

A wave has frequency 50 Hz and wavelength 0.80 m. What is its speed?

A. 40 m s-1 B. 62.5 m s-1 C. 0.016 m s-1 D. 50.8 m s-1

Question 2 (Structured Paper 2 Style)

A sound wave of speed 340 m s-1 has frequency 680 Hz.

(a) Calculate its wavelength. [2 marks]

(b) State whether sound is transverse or longitudinal. [1 mark]