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Turning Points in Physics

Electromagnetic waves

  • 4 things to know
  • Paper 3, section B

Overview

Maxwell's prediction of the speed of light, and Hertz's and Fizeau's confirmations.

What you need to know

Answer each one before you reveal it.

Your recallNot started
Numbers

What is Maxwell's formula for the speed of light, and which constants appear in it?

Numbers

How did Hertz generate and detect radio waves, and how did he measure their wavelength?

Numbers

How did Fizeau's measurement support Maxwell, and why did it matter?

Process

Explain what occurred at the critical rotation speed in Fizeau's toothed wheel experiment

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Describe the orientation of the electric field, magnetic field, and direction of propagation in an electromagnetic wave.

    Model answer

    The electric and magnetic fields oscillate perpendicular to each other and both are perpendicular to the direction of wave propagation.

  2. 2

    Explain how electromagnetic waves are able to propagate through space without requiring a continuous energy source along their path.

    Model answer

    Electromagnetic waves are self-propagating: a changing electric field generates a changing magnetic field, which in turn generates a changing electric field, allowing the wave to sustain itself as it travels.

  3. 3

    Why can electromagnetic waves travel through a vacuum, unlike sound waves?

    Model answer

    Electromagnetic waves require no medium for propagation; they consist of oscillating electric and magnetic fields that can exist and propagate through empty space.

  4. 4

    State Maxwell's expression for how fast electromagnetic waves travel in a vacuum.

    Model answer

    c = 1/√(μ₀ε₀)

  5. 5

    Identify the two physical constants that appear in Maxwell's formula for the speed of electromagnetic waves.

    Model answer

    The permittivity of free space (ε₀) and the permeability of free space (μ₀).

  6. 6

    Explain why the constants ε₀ and μ₀ appearing in Maxwell's formula link electromagnetism to the speed of light.

    Model answer

    These constants describe fundamental electric and magnetic properties of free space; their combination in Maxwell's formula yields the speed of electromagnetic waves, showing that light speed is determined by the electromagnetic properties of the vacuum.

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