Fig 5 shows a logic gate used in a security system for a workshop. The alarm only sounds when a pressure pad (input A) AND a door switch (input B) are both ...
Question 1 Report
Fig 5 shows a logic gate used in a security system for a workshop. The alarm only sounds when a pressure pad (input A) AND a door switch (input B) are both activated at the same time.
(a) Name the logic gate shown in Fig 5. [1]
(b) Complete the truth table for this logic gate. [2]
| Input A | Input B | Output Q |
|---|---|---|
| 0 | 0 | |
| 0 | 1 | |
| 1 | 0 | |
| 1 | 1 |
Answer Details
(a) The logic gate shown in Fig 5 is an AND gate. [1]
The symbol shows the characteristic D-shaped body with a flat back and a curved front. An AND gate produces a high output (logic 1) only when all of its inputs are high simultaneously. This makes it the correct choice for the security system described: the alarm sounds only when both the pressure pad (A) and the door switch (B) are activated at the same time. If either input is low, the output remains low and the alarm stays silent.
(b) Completed truth table: [2]
| Input A | Input B | Output Q |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |
The AND gate outputs 1 only in the final row, where both inputs are 1. In all other combinations, at least one input is 0, so the output remains 0. This truth table confirms that both conditions must be met simultaneously for the alarm to activate.
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