Quelpr
1 markLogic Gates

CAPE Physics Unit 2 · 2005 · Paper 2 · Question 7(b)(i)

A burglar alarm incorporates the latch circuit of Figure VIII with a window switch connected to I_1 and a reset switch connected to I_2.

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), explain how this 'sets' the alarm so that it is ready to be triggered.

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

The mark scheme is shown once you've answered.

Practise this question

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(a)(iv)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…[3 marks]
  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