AQA · GCSE · Physics
Course version: 8463 · Version from Sept 2016
(HT only) When radio waves are absorbed they may create an alternating…
Full specification wording
Properties of electromagnetic waves 2: (HT only) When radio waves are absorbed they may create an alternating current with the same frequency as the radio wave itself, so radio waves can themselves induce oscillations in an electrical circuit.
This is Higher tier, and it is the reverse of the production statement.
Checked against the AQA 8463 specification (opens in a new tab) on .
- Point 2 of 11
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
This is Higher tier, and it is the reverse of the production statement. A radio wave arriving at a receiving aerial carries an oscillating electric field, and that field pushes the free electrons in the metal backwards and forwards. The result is an alternating current in the aerial with exactly the same frequency as the radio wave that produced it, so the information carried by the wave survives the transfer. The receiver circuit is tuned so that it responds strongly to one particular frequency, which is how one station is picked out from the many arriving at once. Transmission and reception are therefore a matched pair: oscillating charges make the wave, and the wave then makes charges oscillate again in the receiver.
What earns the marks
- Saying that the radio wave is absorbed by the aerial.
- Stating that this produces an alternating current in the aerial or circuit.
- Stating that the current has the same frequency as the radio wave.
- Saying that the circuit can be tuned to respond to one particular frequency.
Common mistakes and how to put them right
Saying a direct current is produced in the aerial.
Saying the frequency of the current is higher or lower than that of the wave.
Describing the aerial as reflecting the wave rather than absorbing it.
Explaining reception without mentioning the oscillation of charges in the metal.
Exam tips
- Answer transmission and reception as mirror images of each other; the same sentence works both ways.
- The phrase same frequency as the radio wave is almost always a marking point, so include it.
- Watch the word induce here: it means cause an oscillation, not electromagnetic induction in a generator.
Try the lesson
The start of the Properties of electromagnetic waves 2: (HT only) When radio waves are absorbed they may create an alternating current with the same frequency as the radio wave itself, so radio waves can themselves induce oscillations in an electrical circuit. lesson, made from checked teaching notes for this specification point.
Have a go first
A radio wave of frequency 90 MHz is absorbed by a receiving aerial. What is the frequency of the alternating current produced in the aerial circuit?
Listen
This is Higher tier, and it is the reverse of the production statement. A radio wave arriving at a receiving aerial carries an oscillating electric field, and that field pushes the free electrons in the metal backwards and forwards. The result is an alternating current in the aerial with exactly the same frequency as the radio wave that produced it, so the information carried by the wave survives the transfer. The receiver circuit is tuned so that it responds strongly to one particular frequency, which is how one station is picked out from the many arriving at once. Transmission and reception are therefore a matched pair: oscillating charges make the wave, and the wave then makes charges oscillate again in the receiver. A strong answer earns marks for these points. saying that the radio wave is absorbed by the aerial. stating that this produces an alternating current in the aerial or circuit. stating that the current has the same frequency as the radio wave. saying that the circuit can be tuned to respond to one particular frequency. Exam tip: Answer transmission and reception as mirror images of each other; the same sentence works both ways.
Key words
Say what each word means before you turn the card.
absorption by an aerial
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induced alternating current
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matching frequency
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tuning a receiver
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See every definition
- absorption by an aerial
- The radio wave is absorbed by the aerial, and the oscillating electric field it carries pushes the free electrons in the metal backwards and forwards.
- induced alternating current
- The wave can induce oscillations in an electrical circuit, producing an alternating current in the aerial with exactly the same frequency as the radio wave that produced it.
- matching frequency
- The current has exactly the same frequency as the radio wave, so the information carried by the wave survives the transfer.
- tuning a receiver
- The receiver circuit is tuned so that it responds strongly to one particular frequency, which is how one station is picked out from the many arriving at once.
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