O-LevelComputer ScienceBoolean logic2210/23 · Oct/Nov 2023 · Q611 Marks

There are three descriptions of logic gates. Each logic gate has two inputs A and B with one output X. Identify each logic gate. Complete a truth table for each logic gate.

(a)The only time the output is 1 is when both inputs are 1. Logic gate Complete the truth table for this description. A B X 0 0 0 1 1 0 1 1[2]
(b)The output is 1 when both inputs are different. Logic gate Complete the truth table for this description. A B X 0 0 0 1 1 0 1 1[2]
(c)The only time the output is 1 is when both inputs are 0. Logic gate Complete the truth table for this description. A B X 0 0 0 1 1 0 1 1[2]
(d)Consider this logic expression: X = (NOT A OR NOT B) OR NOT C Draw a logic circuit for this logic expression. Each logic gate must have a maximum of two inputs. Do not attempt to simplify this logic expression.[5]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2023). The mark or mark type is shown in brackets.

[2] One mark for correct gate and one mark for correct truth table AND A B X 0 0 0 0 1 0 1 0 0 1 1 1
[2] One mark for correct gate and one mark for correct truth table XOR // EOR A B X 0 0 0 0 1 1 1 0 1 1 1 0
[2] One mark for correct gate and one mark for correct truth table NOR A B X 0 0 1 0 1 0 1 0 0 1 1 0
[5] One mark for each correct gate, with the correct input(s) as shown. [Diagram description: NOT gate for A, NOT gate for B. Outputs of these NOT gates go into an OR gate. The output of this OR gate then goes into another OR gate, along with the output of a NOT gate for C. The final OR gate produces X. Each gate must have max two inputs. This means: (NOT A) -> OR1, (NOT B) -> OR1. (Output OR1) -> OR2, (NOT C) -> OR2. (Output OR2) -> X]

On Oracle Prep you can write or photograph your own answer and have it marked by AI against this mark scheme, with feedback on what you missed.