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EMF and internal resistanceAQA A-Level Physics: Flashcards

What these 12 flashcards ask

  • Define emf.
  • What is the terminal pd?
  • Why is the terminal pd less than the emf when current flows?
  • State the circuit equation involving emf and internal resistance.
  • What are lost volts?
  • When does the terminal pd equal the emf?
  • What is the short-circuit current of a cell?
  • Give the expression for power wasted inside a cell.
  • What are the emf and internal resistance of n identical cells in series?
  • What are the emf and internal resistance of n identical cells in parallel?
  • In Required practical 6, what do you plot and what do you obtain?
  • Why disconnect the circuit between readings in the practical?

Exam questions on EMF and internal resistance

  1. A cell of emf 1.5 V and internal resistance 0.50 Ω is connected in series with a resistor of resistance 2.5 Ω.
    Calculate the energy dissipated in the internal resistance of the cell in 1.0 minute.2 marks
  2. A car battery of emf 12.6 V and internal resistance 0.020 Ω is used to start an engine. While the engine is being started the starter motor draws a current of 150 A from the battery.
    Calculate the rate at which energy is dissipated inside the battery and state the form of the energy.2 marks
  3. A student investigates a cell using a variable resistor, an ammeter and a voltmeter. The terminal pd V is measured for a range of currents I. The points lie on a straight line: V = 1.38 V when I = 0.20 A and V = 1.14 V when I = 0.60 A.
    Use the readings to determine the emf and the internal resistance of the cell.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).