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4 marksTransducers

CAPE Physics Unit 2 · 2007 · Paper 2 · Question 2(a)

An operational amplifier is connected as a temperature sensor in a comparator circuit with a thermistor, fixed resistors, and an LED indicator. Table 2 provides thermistor resistance R at various temperatures θ.

Plot a graph of resistance R against temperature θ on the grid provided.

This question uses a figure or table from the paper — you'll see it when you practise.

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Other parts of this question

  1. 2(b)(i)Use your graph to determine the resistance of the thermistor at 75 °C.[1 mark]
  2. 2(b)(ii)State, with reasons, whether the LED will be ON or OFF when the temperature of the thermistor is 75 °C.[3 marks]
  3. 2(b)(iii)Determine the temperature at which the LED turns on as the temperature is increased from 40 °C.[2 marks]

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