GCSE Physics 05 — Light and Electromagnetic Waves

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Topics include Properties of Electromagnetic Waves, The Wave Equation and Frequency, Reflection of Light, Refraction of Light, Total Internal Reflection (TIR), Lenses: Types and Ray Diagrams, Lenses: Images, Magnification, and Power, and Visible Light: Colour, Filters, and Dispersion.

Physics EN

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The Wave Equation and Frequency

The relationship between wave speed, frequency, and wavelength allows for the calculation of unknown wave properties.

Key points

The Wave Equation: $v = f \lambda$
$v$ = wave speed (m/s) (usually $3 \times 10^8$ for EM waves in a vacuum).
$f$ = frequency (Hz).
$\lambda$ = wavelength (m).
Relationships: If speed is constant, frequency and wavelength are inversely proportional (as $f$ increases, $\lambda$ decreases).

Worked example

Question

A radio station broadcasts at a frequency of 100 MHz. Calculate the wavelength of these radio waves. (Speed of light

c = 3 \times 10^8\,\text{m/s}

Solution

1. Convert frequency to Hz:

100\,\text{MHz} = 100 \times 10^6\,\text{Hz} = 1 \times 10^8\,\text{Hz}

.
2. Rearrange formula:

\lambda = \frac{v}{f}

.
3. Substitute values:

\lambda = \frac{3 \times 10^8}{1 \times 10^8}

.
4. Calculate:

\lambda = 3\,\text{m}

Common pitfalls

Forgetting to convert units (e.g., MHz to Hz, nm to m).
Thinking speed changes when frequency changes in a vacuum (speed is constant; wavelength changes).

Prerequisites

Standard form calculations
Rearranging equations

Further resources

BBC Bitesize GCSE Physics: The Wave Equation and Frequency
Clear GCSE-level explanations and practice questions.

BBC Bitesize · article