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Potential dividersAQA A-Level Physics: Flashcards

What these 12 flashcards ask

  • State the potential divider equation.
  • Why does a potential divider share the pd in proportion to resistance?
  • How must a variable resistor be connected to give 0 V to the full supply pd?
  • What happens to the resistance of an LDR as light intensity increases?
  • What happens to the resistance of an NTC thermistor as temperature increases?
  • LDR on top, fixed resistor below, output across the fixed resistor. What happens to the output in the dark?
  • How can the behaviour of the divider be reversed?
  • What happens to the output pd if a load is connected across the output?
  • When is the effect of loading small?
  • A divider has 4.0 kΩ and 2.0 kΩ across 6.0 V. What is the pd across the 2.0 kΩ resistor?
  • Why do switching circuits often have very high input resistance?
  • What is a rheostat?

Exam questions on Potential dividers

  1. A potential divider consists of a 6.0 kΩ resistor in series with a 3.0 kΩ resistor connected across a 9.0 V supply of negligible internal resistance. The output is taken across the 3.0 kΩ resistor.
    Explain why connecting the load across the output reduces the output pd.2 marks
  2. A light-dependent resistor (LDR) is connected in series with a fixed 2.2 kΩ resistor across a 5.0 V supply of negligible internal resistance, forming a potential divider that controls a street lamp. The output is taken across the fixed resistor. The resistance of the LDR is 500 Ω in bright light and 20 kΩ in darkness.
    Calculate the output pd in darkness.2 marks
  3. A designer needs to supply a motor with a variable pd from 0 V to 12 V from a 12 V supply of negligible internal resistance. A variable resistor with a track of total resistance 100 Ω and a sliding contact is available.
    Describe how the variable resistor should be connected so that it acts as a potential divider supplying a pd that can be varied from 0 V to 12 V.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).