A monochromatic electromagnetic wave in free space has wavelength $0.12$ m. Calculate its frequency and the speed of propagation.

easy 1 mark Class 12 · Physics · Electromagnetic Waves

Answer

Speed =

3.0 \times 1 0^{8}

m/s, Frequency =

2.5 \times 1 0^{9}

Hz.

The correct answer is Speed = $3.0 \times 1 0^{8}$ m/s, Frequency = $2.5 \times 1 0^{9}$ Hz. — Compute $f = 3.0 \times 1 0^{8} /0.12 = 2.5 \times 1 0^{9}$ Hz.

Step-by-step solution

Speed of light in vacuum is $c = 3.0 \times 1 0^{8} m/s$ .
Use the relation $f = c / l amb d a$ with $l amb d a = 0.12$ m.
Compute $f = 3.0 \times 1 0^{8} /0.12 = 2.5 \times 1 0^{9}$ Hz.

Common mistake: Confusing wavelength with frequency or forgetting units

Concept tested: Speed and frequency of EM waves in free space

Published 4 September 2026 · Last updated 16 September 2026 · How this solution was prepared and checked

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A monochromatic electromagnetic wave in free space has wavelength 0.12 m. Calculate its frequency and the speed of propagation.

Step-by-step solution

A monochromatic electromagnetic wave in free space has wavelength $0.12$ m. Calculate its frequency and the speed of propagation.