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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
Question 2
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°
Answer
The graph should begin at a maximum amplitude when the dipole receiver is aligned with the dipole transmitter (0°). As the receiver is rotated to 90°, the amplitude decreases to zero since it is perpendicular to the transmitter. From 90° to 180°, the amplitude increases back to a maximum again and then decreases to zero at 270° before rising back to a maximum at 360°. The pattern should resemble a sine wave and curve rather than sharp spikes, indicating the periodic nature of the amplitude response for each 180° rotation.
Step 2
Explain, using a suitable calculation, why this leads to the conclusion that light is an electromagnetic wave.
Answer
Starting from Maxwell's equation for the speed of electromagnetic waves:
With (\mu_0 = 4\pi \times 10^{-7} \ , \text{T m/A}) and (\epsilon_0 = 8.85 \times 10^{-12} \ , \text{F/m}), substituting these values gives:
This calculated speed of light agrees with measured values, thus supporting the conclusion that light behaves as an electromagnetic wave.