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Electrical power and I-V characteristicsEdexcel International A Level Physics: Flashcards

What these 12 flashcards ask

  • Give the equation for electrical power in terms of V and I.
  • Give the equation for energy transferred using V, I and t.
  • Derive P = I²R.
  • Derive P = V²/R.
  • When is P = V²/R the best form to use?
  • What does the I–V graph of an ohmic conductor look like?
  • Describe the I–V graph of a filament lamp.
  • Why does a filament lamp's resistance rise as it heats?
  • What happens to the resistance of an NTC thermistor as temperature rises?
  • Describe the I–V graph of a diode.
  • Why is a protective resistor used with a diode?
  • What is thermal runaway in a thermistor at constant p.d.?

Exam questions on Electrical power and I-V characteristics

  1. A 230 V electric heater has a heating element of resistance 46 Ω. It is connected to a 230 V mains supply and works at its normal operating temperature.
    Calculate the current in the heater and use it to show that P = I²R gives the same power as in part (a).2 marks
  2. A technician investigates an unmarked electrical component in a sealed box with two terminals. With the potential difference applied in one direction, the current is almost zero until the p.d. reaches about 0.7 V, after which the current rises very rapidly for small further increases in p.d. With the p.d. reversed, the current stays almost zero up to 5.0 V.
    At a forward p.d. of 0.80 V the current in the component is 20 mA. Calculate the power dissipated and the resistance at this p.d.2 marks
  3. A filament lamp is labelled 12 V, 36 W. It is operated at its rated p.d. from a 12 V supply of negligible internal resistance. The resistance of the filament when cold, at room temperature, is measured as 0.40 Ω.
    Calculate the current in the lamp at its rated p.d., the resistance of the filament at this p.d. and the energy transferred in 2.0 minutes.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).