In 1864, James Clerk Maxwell published a theory that included an equation for the speed of electromagnetic waves in a vacuum - AQA - A-Level Physics - Question 2 - 2021 - Paper 7

In this experiment, the radio wave transmitter T generates an oscillating current, which creates an alternating electric field (E-field) and magnetic field (B-field) perpendicular to each other and to the direction of wave propagation, consistent with Maxwell's model of electromagnetic waves.

The oscillating current in T induces a horizontal electric field that propagates through space. As this E-field varies, it induces a magnetic field around the conductive loop aerial D. The varying magnetic field generates an electromotive force (emf) in the loop aerial.

This implies that electromagnetic waves can transmit energy through space, as the oscillating E-field creates a corresponding B-field, enabling energy transfer between the transmitter and the detector via the space between them.

In the given experimental setup, stationary waves form between the fixed transmitter and the fixed reflector. The distance between them is approximately 12 m and the transmitter frequency is 75 MHz.

The wavelength ($\lambda$) can be calculated using:
$\lambda = \frac{C}{f}$
where $C \approx 3 \times 10^8 \text{m/s}$ and $f = 75 \times 10^6 \text{Hz}$.
Calculating gives us:

$\lambda = \frac{3 \times 10^8}{75 \times 10^6} = 4 \text{m}$

Since the distance between the transmitter and the reflector is greater than half of the wavelength (i.e., greater than 2m), this arrangement can indeed be used to measure the speed of electromagnetic waves as suggested by Maxwell's equation.