Electromagnetic waves (A-level only) Flashcards – AQA A-level Physics (7408)

What is an electromagnetic wave composed of?

Oscillating electric and magnetic fields that propagate through space.

How are the fields oriented in a plane electromagnetic wave, and what does this imply about its wave type?

The fields are perpendicular to each other and to the direction of propagation, so the wave is transverse.

Do electromagnetic waves require a material medium to travel?

No. They can travel through a vacuum.

What do electromagnetic waves carry?

Energy.

What is Maxwell’s formula for the speed of electromagnetic waves in a vacuum in terms of the permittivity and permeability of free space?

$c = \frac{1}{\sqrt{\mu_0\varepsilon_0}}$

Here $\varepsilon_0$ is the permittivity and $\mu_0$ the permeability of free space.

For a fixed charge distribution, how is electric field strength related to the permittivity of free space, $\varepsilon_0$?

Electric field strength is inversely proportional to $\varepsilon_0$.

For a fixed wire geometry and current, how is magnetic flux density related to the permeability of free space, $\mu_0$?

Magnetic flux density is proportional to $\mu_0$.

How did Hertz generate radio waves?

Oscillations in a transmitting electrical circuit with a spark gap produced electromagnetic waves.

What evidence showed that Hertz’s receiving circuit detected radio waves?

A spark appeared in the separate receiving circuit.

How did Hertz use wavelength and frequency to determine radio-wave speed?

He used $v = f\lambda$.

What did Hertz’s measured radio-wave speed suggest about radio waves and light?

The speed was consistent with the speed of light, supporting the view that both are electromagnetic waves.