Question 1

A game uses three sensors. A red light (R) in the game switches on if **all** of the following conditions are true:
- sensor D is off
- sensor L is on
- sensor W is on.
Complete the logic circuit for this game. You **must** use the correct symbols for the logic gates.

Accepted Answer

1.  **Analyze the conditions:**
    *   "sensor D is off": This means we need the logical opposite of D, which is NOT D. This requires a NOT gate for input D.
    *   "sensor L is on" and "sensor W is on": These inputs are used as they are.
    *   "**all** of the following conditions are true": The word "all" implies an AND condition. We need a gate that outputs true only when all its inputs are true. This is an AND gate.
2.  **Construct the circuit:**
    *   Draw an input line for D and connect it to a NOT gate.
    *   Draw input lines for L and W.
    *   Take the output from the NOT gate (which is NOT D), the input line for L, and the input line for W, and connect all three to the inputs of a single 3-input AND gate.
    *   Connect the output of the AND gate to the output R.

Question 2

What mistakes do candidates make on this AQA GCSE question?

Accepted Answer

✗ Using the wrong logic gate symbols (e.g., American vs IEC standard if not specified, but consistency is key).
✗ Using an OR gate instead of an AND gate.
✗ Forgetting the NOT gate for input D.
✗ Using three separate 2-input AND gates instead of one 3-input AND gate.

A game uses three sensors. A red light (R) in the game switches on if all of the following conditions are true:

sensor D is off

sensor L is on

sensor W is on.
Complete the logic circuit for this game. You must use the correct symbols for the logic gates.

How to approach this question

Full Answer

Common mistakes

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