An automated inspection trolley in a railway depot receives radio instructions from a fixed control unit. Its receiving circuit can be tuned to different frequencies.
A technician gives this description.
‘The radio wave carries electrons from the control unit to the trolley. When these electrons arrive, they flow steadily around the receiving circuit. Changing the tuning of the receiving circuit cannot affect the size of its response.’
Explain the errors in the technician's description.
A technician tests the radio link. The transmitter output is unchanged during the tests.
| Test | Transmitter oscillation frequency | Distance between control unit and trolley | Signal voltage in receiving circuit |
|---|---|---|---|
| 1 | 0.80 MHz | 25 m | 120 μV120\ \mu\text{V}120 μV |
| 2 | 1.60 MHz | 25 m | 120 μV120\ \mu\text{V}120 μV |
| 3 | 0.80 MHz | 75 m | 40 μV40\ \mu\text{V}40 μV |
The technician next sets the transmitter to 1.60 MHz and places the trolley 75 m from the control unit.
Assume that the patterns in the results continue. Explain the frequency and signal voltage expected in the receiving circuit.
The trolley's receiver is set to 1.25 MHz. Two channels are available.
| Channel | Wavelength |
|---|---|
| P | 60 m |
| Q | 240 m |
The speed of radio waves in air is 3.0 × 108 m s-1.
Calculate the frequency of the radio wave for each channel. State which channel the receiver will select.
104 exam-style questions on Edexcel GCSE Physics 5.4 Uses and dangers of EM radiation, covering 5.4.1 Dangers of electromagnetic radiation, 5.4.2 Uses of electromagnetic radiation, 5.4.3 Radio waves and oscillations in circuits, and 5.4.4 Changes in atoms and nuclei generating radiation. Each one has a worked solution and a mark scheme showing where the marks go.