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3 marksTransducers

CAPE Physics Unit 2 · 2018 · Paper 2 · Question 2(d)

The LDR is used in an automatic switching circuit for floodlights as shown in Figure 3.

Use your graph from (c) to find the resistance of the LDR at a luminous intensity of 200 cd.

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Other parts of this question

  1. 2(a)State the meaning of the acronym LDR, and briefly explain its operation.[4 marks]
  2. 2(b)Complete Columns 3 and 4 of Table 2 (log₁₀ R and log₁₀ Iᵥ).[2 marks]
  3. 2(c)On the grid provided in Figure 2, plot a graph of log₁₀ R against log₁₀ Iᵥ and draw the line of best fit through the points.[4 marks]
  4. 2(e)If the switching circuit turns on the floodlights whenever the voltage at its input falls below 7.5 volts, what should the value of R be?[2 marks]

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