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3 marksLogic Gates

CAPE Physics Unit 2 · 2013 · Paper 2 · Question 5(a)

An automatic headlight system turns on headlights when ambient light falls below a threshold, ignition switch S1 (logic A) is ON, and headlights AUTO switch S2 (logic B) is ON. Light level below threshold is logic C = 0.

Use logic Y to represent the output of this system and draw up the truth table for the operation of the headlight automatic switching circuit. Write the logic equation represented by this truth table.

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Other parts of this question

  1. 5(b)(i)In this circuit, the open loop operational amplifier is used to compare the surrounding lighting level with a preset value. Explain how this is done.[3 marks]
  2. 5(b)(ii)Justify the need for the light dependent resistor (LDR) in the circuit.[2 marks]
  3. 5(b)(iii)Describe how a relay functions, stating why this device is necessary in the circuit.[2 marks]
  4. 5(c)(i)Replace the circuit in the dashed box, P, with one consisting of NAND gates only.[3 marks]
  5. 5(c)(ii)The 7400 chip has 4 NAND gates. How many 7400 chips are required for the NAND-equivalent circuit drawn in Part c (i)?[2 marks]

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