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Alternating currentsEdexcel A-Level Physics: Flashcards

What these 13 flashcards ask

  • Define the period of an alternating supply.
  • Define the frequency of an alternating supply.
  • State the relationship between frequency and period.
  • What is the peak value of an alternating p.d.?
  • What is the peak-to-peak value in terms of the peak value?
  • What is meant by the r.m.s. value of an alternating current?
  • State the relationship between r.m.s. and peak p.d. for a sinusoidal supply.
  • State the relationship between r.m.s. and peak current for a sinusoidal supply.
  • What is the peak p.d. of 230 V r.m.s. mains?
  • How is the mean power in a resistor calculated from the r.m.s. p.d.?
  • How does the peak power in a resistor compare with the mean power?
  • Why does the r.m.s. value allow a fair comparison of a.c. with d.c.?
  • How do you find the frequency from an oscilloscope trace?

Exam questions on Alternating currents

  1. A sinusoidal alternating p.d. has a peak value of 12.0 V and a frequency of 50 Hz.
    Explain what is meant by the root-mean-square value of an alternating p.d., and why it is less than the peak value.2 marks
  2. A heater of resistance 46 Ω is connected to the 230 V r.m.s. mains supply, which has a frequency of 50 Hz.
    Calculate the r.m.s. current in the heater and the peak current.2 marks
  3. A student displays an alternating supply on an oscilloscope. The time-base is set to 5.0 ms per division and the Y-gain to 2.0 V per division. One complete cycle of the trace spans 4.0 horizontal divisions, and the trace reaches 3.0 divisions above and 3.0 divisions below the centre line.
    Calculate the period and the frequency of the alternating supply.3 marks
See the full worksheet

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).