Logic circuits and the AND gate
Answers are for parents and teachers.
1
A greenhouse sprinkler runs only when the water valve is open and the pump is on. Name the inputs and the output and write the truth table with rows in counting order.
Inputs: valve open (A), pump on (B). Output: the sprinkler runs (Y). Rows 00, 01, 10, 11 give 0, 0, 0, 1.
2
How many rows does the truth table of an AND gate with six inputs have, and how many of them have the output 1?
64 rows (2⁶ = 64); exactly one has the output 1, the row of six 1s.
3
A pupil says: “For A = 1 and B = 1 the AND output is 2, because 1 + 1 = 2.” Correct the sentence.
The values of a gate are only 0 and 1. AND is like multiplication: 1·1 = 1, so the output is 1.
4
Three switches are in a row and the middle one is open. Is the lamp lit? Why?
No. The path is broken at the middle switch, whatever the other two do.
5
Write the rows of a three-input table in counting order, from 000 to 111.
000, 001, 010, 011, 100, 101, 110, 111.