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Figure 2 shows a modern version of the apparatus used by Hertz to investigate the properties of electromagnetic waves - AQA - A-Level Physics - Question 2 - 2018 - Paper 7

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Figure 2 shows a modern version of the apparatus used by Hertz to investigate the properties of electromagnetic waves. Electromagnetic waves are continuously emitted... show full transcript

Worked Solution & Example Answer:Figure 2 shows a modern version of the apparatus used by Hertz to investigate the properties of electromagnetic waves - AQA - A-Level Physics - Question 2 - 2018 - Paper 7

Step 1

Sketch a graph on Figure 4 to show how the amplitude detected by the dipole receiver varies with angle of rotation as the receiver is turned through 360°.

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Answer

The graph should start at the maximum amplitude when the receiver is aligned with the dipole transmitter. As the angle of rotation increases from 0° to 180°, the amplitude decreases and reaches a minimum at 90°, followed by a return to maximum amplitude as it completes 360°. The graph should show periodicity with peaks (maxima) at 0°, 180° and troughs (minima) at 90° and 270° indicating the oscillating nature of the detected signal.

Step 2

Explain, using a suitable calculation, this equation led to the conclusion that light is an electromagnetic wave.

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Answer

Maxwell's equation indicates that the speed of electromagnetic waves can be derived from the constants of permeability and permittivity. If we use the values: μ0≈4π×10−7 H/m\mu_0 \approx 4\pi \times 10^{-7} \text{ H/m} and ϵ0≈8.85×10−12 F/m\epsilon_0 \approx 8.85 \times 10^{-12} \text{ F/m}, substituting these into the equation gives:

c=1(4π×10−7)(8.85×10−12)≈3.0×108 m/sc = \frac{1}{\sqrt{(4\pi \times 10^{-7})(8.85 \times 10^{-12})}} \approx 3.0 \times 10^8 \text{ m/s}

This value matches the measured speed of light, thus supporting the conclusion that light travels as an electromagnetic wave.

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