AQA · A-Level · Physics

    Course version: 7408 · Version from Sept 2016

    Hertz’s discovery of radio waves including measurements of the speed of…

    Full specification wording

    Electromagnetic waves (A-level only): Hertz’s discovery of radio waves including measurements of the speed of radio waves.

    Hertz generated and detected radio waves using a spark-gap transmitter and a resonant loop receiver.

    Checked against the AQA 7408 specification (opens in a new tab) on .

    • Point 2 of 3
    • 4 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    Hertz generated and detected radio waves using a spark-gap transmitter and a resonant loop receiver. A high-voltage spark across a gap produced oscillating charges, radiating electromagnetic waves. When the receiver loop was tuned to the same frequency, small sparks appeared across its gap, demonstrating reception. Hertz showed the waves could be reflected, refracted and polarised, confirming their electromagnetic nature. He measured their speed by relating wavelength to frequency: he determined wavelength from standing-wave patterns or interference and frequency from the transmitter circuit, then used v = fλ. His results agreed with the speed of light, supporting Maxwell’s prediction that light is an electromagnetic wave.

    What earns the marks

    • Hertz used a spark-gap transmitter to generate radio waves and a resonant loop receiver to detect them.
    • Detection relied on tuning the receiver to the transmitter frequency so that resonance produced detectable sparks.
    • Hertz demonstrated reflection, refraction and polarisation of radio waves, supporting their electromagnetic wave nature.
    • He measured wavelength using standing waves or interference and frequency from the transmitter, then calculated speed using v = fλ.
    • The measured speed was close to the speed of light, providing evidence that light is an electromagnetic wave.
    • Hertz’s work confirmed Maxwell’s theoretical prediction of electromagnetic waves.

    Common mistakes and how to put them right

    • Thinking Hertz discovered radio waves by accident without measurement.

      Put it right by stating he deliberately generated, detected and measured their speed.

    • Confusing the roles of transmitter and receiver.

      Put it right by stating the spark-gap transmitter radiates and the loop receiver detects via resonance.

    • Using c = fλ with the measured frequency and wavelength without recognising that the result is compared with the speed of light.

      Put it right by stating the comparison supports Maxwell’s theory.

    Exam tips

    • Describe the apparatus clearly: spark gap, induction coil, loop with small gap, and how sparks indicate detection.
    • Explain how wavelength was found from the distance between nodes or interference fringes, and frequency from the oscillator circuit.
    • Link the measured speed to the speed of light to explain the significance for Maxwell’s theory.

    Try the lesson

    The start of the Electromagnetic waves (A-level only): Hertz’s discovery of radio waves including measurements of the speed of radio waves. lesson, made from checked teaching notes for this specification point.

    Have a go first

    In Hertz’s experiments with radio waves, what did he use to detect the radio waves produced by his spark gap?

    Listen

    Hertz generated and detected radio waves using a spark-gap transmitter and a resonant loop receiver. A high-voltage spark across a gap produced oscillating charges, radiating electromagnetic waves. When the receiver loop was tuned to the same frequency, small sparks appeared across its gap, demonstrating reception. Hertz showed the waves could be reflected, refracted and polarised, confirming their electromagnetic nature. He measured their speed by relating wavelength to frequency: he determined wavelength from standing-wave patterns or interference and frequency from the transmitter circuit, then used v = fλ. His results agreed with the speed of light, supporting Maxwell’s prediction that light is an electromagnetic wave. A strong answer earns marks for these points. Hertz used a spark-gap transmitter to generate radio waves and a resonant loop receiver to detect them. Detection relied on tuning the receiver to the transmitter frequency so that resonance produced detectable sparks. Hertz demonstrated reflection, refraction and polarisation of radio waves, supporting their electromagnetic wave nature. He measured wavelength using standing waves or interference and frequency from the transmitter, then calculated speed using v = fλ. A common slip: Thinking Hertz discovered radio waves by accident without measurement. Instead, stating he deliberately generated, detected and measured their speed. Exam tip: Describe the apparatus clearly: spark gap, induction coil, loop with small gap, and how sparks indicate detection.

    See it

    A top-down flowchart of nine boxes linked by arrows. The first box says the spark-gap transmitter generates radio waves, leading to a resonant loop receiver tuned to the same frequency. The next box says small sparks at the receiver gap show detection. Then the waves are shown to reflect, refract and polarise. Next, wavelength is found from standing waves or interference, and frequency is taken from the transmitter circuit. Speed is then calculated using v = fλ. The next box says the speed is close to the speed of light, and the final box says this supports Maxwell's prediction that light is an electromagnetic wave.
    It shows the sequence of Hertz's method, from generating and detecting radio waves through measuring their speed to confirming Maxwell's prediction.

    Key words

    Say what each word means before you turn the card.

    Experimental generation and detection of radio waves

    Try answering aloud or in your head before turning the card.

    Resonance in receiver circuits

    Try answering aloud or in your head before turning the card.

    Measurement of speed using v = fλ

    Try answering aloud or in your head before turning the card.

    Evidence for Maxwell’s electromagnetic theory of light

    Try answering aloud or in your head before turning the card.

    See every definition
    Experimental generation and detection of radio waves
    A high-voltage spark across a gap produced oscillating charges that radiated electromagnetic waves, and a resonant loop receiver tuned to the same frequency showed small sparks across its gap.
    Resonance in receiver circuits
    Detection relied on tuning the receiver to the transmitter frequency so that resonance produced detectable sparks.
    Measurement of speed using v = fλ
    Wavelength was determined from standing-wave patterns or interference and frequency from the transmitter circuit, then speed was calculated using v = fλ.
    Evidence for Maxwell’s electromagnetic theory of light
    The measured speed agreed with the speed of light, supporting Maxwell’s prediction that light is an electromagnetic wave.

    Label the diagram

    Some boxes have lost their names. Pick the right name for each number.

    The diagram again, with 3 boxes numbered instead of named. A top-down flowchart of nine boxes linked by arrows. The first box says the spark-gap transmitter generates radio waves, leading to a resonant loop receiver tuned to the same frequency. The next box says small sparks at the receiver gap show detection. Then the waves are shown to reflect, refract and polarise. Next, wavelength is found from standing waves or interference, and frequency is taken from the transmitter circuit. Speed is then calculated using v = fλ. The next box says the speed is close to the speed of light, and the final box says this supports Maxwell's prediction that light is an electromagnetic wave.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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