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3 marksLogic Gates

CAPE Physics Unit 2 · 2005 · Paper 2 · Question 7(a)(iv)

Analysis of a bistable latch circuit with two cross-coupled NOR gates.

By considering the role of feedback in this circuit and the condition for the gate to have a logic 0 output, explain why the output does not change when the input changes in the second step of the sequence (Row 2) in Table 4.

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Other parts of this question

  1. 7(a)(i)What is the name given to this type of circuit?[1 mark]
  2. 7(a)(ii)Name the logic gate used in the circuit and write out its truth table.[2 marks]
  3. 7(a)(iii)Copy and complete the sequential truth table (Table 4) to show the action of the circuit in Figure VIII.[2 marks]
  4. 7(b)(i)Before going to bed the householder closes the window and presses and releases the reset switch. Making reference to the sequential truth table in 7(a)(iii),…[1 mark]
  5. 7(b)(ii)Why does the alarm sound when a burglar opens the window?[1 mark]
  6. 7(b)(iii)Explain why the alarm stays on even when the burglar closes the window.[1 mark]
  7. 7(b)(iv)How does the householder turn off the alarm?[1 mark]
  8. 7(c)(i)Draw the circuit for a half-adder. Explain, with the aid of a truth table, what its function is and how it performs that function.[4 marks]
  9. 7(c)(ii)Draw a table to show the outputs at points P, Q, R and S for the input states: A. I_1 = 1, I_2 = 0, I_3 = 1; B. I_1 = 1, I_2 = 1, I_3 = 1.[4 marks]

More practice: the rest of this paper · more Logic Gates questions · all CAPE Physics Unit 2 past papers