Answer on paper first, then reveal the mark scheme one mark at a time.
(a) Complete the truth table for the three logic gates. [3]
| A | B | A.B | A + B | A ⊕ B |
|---|---|---|---|---|
| 0 | 0 | |||
| 0 | 1 | |||
| 1 | 0 | |||
| 1 | 1 |
(b) State the output of 1.0. [1]
The diagram shows a logic circuit.
(a) Write a Boolean expression for the output Q. [2]
(b) Complete the truth table for the circuit. [3]
| A | B | C | Q |
|---|---|---|---|
| 0 | 0 | 0 | |
| 0 | 0 | 1 | |
| 0 | 1 | 0 | |
| 0 | 1 | 1 | |
| 1 | 0 | 0 | |
| 1 | 0 | 1 | |
| 1 | 1 | 0 | |
| 1 | 1 | 1 |
A shop alarm (Q) sounds if the door is open (D = 1) and the system is set (S = 1), or at any time the panic button is pressed (P = 1).
(a) Write a Boolean expression for Q. [2]
(b) A student writes the expression Q = D.(S + P). Give one set of input values for D, S and P for which the student's expression gives a different output to the correct expression, and state both outputs. [2]
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