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Alternating currentsAQA A-Level Physics: Flashcards

What these 12 flashcards ask

  • What is the peak-to-peak value of a sinusoidal voltage?
  • Define the rms value of an alternating current.
  • State the relation between Irms and I₀ for a sinusoid.
  • State the relation between Vrms and V₀ for a sinusoid.
  • What is the peak voltage of 230 V rms mains?
  • What is the peak-to-peak voltage of 230 V rms mains?
  • What is the mean value of a sinusoidal voltage over a cycle?
  • Why is the rms value used rather than the mean?
  • What is the mean power in terms of peak values for a resistor?
  • How do you find the voltage from an oscilloscope trace?
  • How do you find the frequency from an oscilloscope trace?
  • What does the time-base control set?

Exam questions on Alternating currents

  1. A heating element of resistance 46 Ω is connected to the UK mains supply, which has an rms voltage of 230 V and a frequency of 50 Hz. The supply voltage is sinusoidal.
    Explain why the mean power dissipated in the element is half of its maximum instantaneous power.2 marks
  2. An oscilloscope is used to display a sinusoidal alternating voltage. The Y-gain is set to 2.0 V per division and the time-base to 5.0 ms per division. The trace has a peak-to-peak height of 5.2 divisions, and one complete cycle of the trace occupies 4.0 divisions horizontally.
    Calculate the rms voltage of the signal.2 marks
  3. A signal generator supplies a sinusoidal alternating current of peak value 1.5 A and frequency 400 Hz to a resistor of resistance 12 Ω.
    Calculate the rms current and the mean power dissipated in the resistor.3 marks
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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).