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Potential dividersEdexcel International A Level Physics: Flashcards

What these 12 flashcards ask

  • What is a potential divider?
  • Give the potential divider equation.
  • Why is the p.d. shared in proportion to resistance?
  • How do you find an unknown resistor in a divider?
  • Why must the output voltmeter have a very high resistance?
  • How does the resistance of an NTC thermistor change with temperature?
  • How does the resistance of an LDR change with light intensity?
  • A thermistor is in series with a fixed resistor; the output is across the fixed resistor. What happens as it heats?
  • What happens to the output if it is taken across the thermistor instead?
  • What happens to Vout if the lower resistor of a divider is increased?
  • The p.d.s across the resistors in a divider must add to what?
  • In dim light an LDR's resistance is large. How does that affect a divider with the output across the LDR?

Exam questions on Potential dividers

  1. A 9.0 V supply of negligible internal resistance is connected across a 2.0 kΩ resistor in series with a 4.0 kΩ resistor. A voltmeter of very high resistance measures the output p.d. across the 4.0 kΩ resistor.
    Calculate the current in the resistors and the power dissipated in the 4.0 kΩ resistor.2 marks
  2. A light-meter circuit has a 6.0 V supply of negligible internal resistance, a light-dependent resistor (LDR) and a 10 kΩ fixed resistor, all in series. The output p.d. is measured across the fixed resistor with a voltmeter of very high resistance. In bright light the LDR has a resistance of 2.0 kΩ; in dim light its resistance is 40 kΩ.
    Calculate the p.d. across the LDR in dim light.2 marks
  3. A temperature-sensing circuit has an NTC thermistor in series with a 4.0 kΩ fixed resistor across a 5.0 V supply of negligible internal resistance. The output p.d. is taken across the fixed resistor. At 20 °C the resistance of the thermistor is 12 kΩ and at 60 °C it is 1.0 kΩ.
    Calculate the output p.d. of the circuit at 20 °C.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).