# 05 - Logic circuit diagrams #2

1. Explain why the red box has an output of a 0?

Because the input B is a 1 and 1 which converts to a 0

It shouldn't be a 0, it should be a 1

Because the input B is 1 and it is going through an OR gate along with a 0 to become a 0

Because the input B is 1, and it is inverted by the NOT gate to 0

2. When creating a truth table for logic gates it is important to test for all possible inputs. What do you notice about the inputs in red?

The inputs are different combinations of 1s and 0s but it doesn't test every combination

They are all random binary numbers input to test different combinations of 0s and 1s

The inputs are all in decimal numbers

The tests go from 0 to 3 in Binary e.g. 0 = 00, 1 = 01, 2=10, and 3 = 11. Doing this ensures all inputs are tested

3. What is the output C? What goes in the question mark?

4

2

1

0

4. Read the excerpt below, examining the circuit and truth table, and fill in the blanks.
```Example of a three input AND gate.
==================================
Notice that the truth table for the three
input gate is similar to the truth table for the two
input gate.

It works on the same principle, this time ______________?
need to be high (1) to get a high output.```

zero inputs

one input

just two inputs

all three inputs

5. For the following circuit, if the inputs for A, B and C are all zero (0), what is the output at X?

Both 0 and 1

1

0

Neither 0 or 1

Each of the sensors are ‘0’ (false = off). This means that they have not detected an intruder. The alarm would not sound

None of the above

Each of the sensors are 0 (False = Off) but are inverted via a NOT gate, which means the alarm would sound

Each of the sensors are '0' (True = On). This means that the alar would sound

7. A burglar has entered via one of the windows. The output at '?' would be 0, the system does not work and the alarm would NOT sound.

True

False

8. If the inputs for A, B and C are all 1, what is the final output (X)?

Both 0 and 1

0

A 1 and a 1

1

9. If the inputs for A, B and C are all 0, what is the final output (X)?

C

1

A

0

10. If the inputs for A, B and C are all 1, what is the final output (X)?

B

A

1

0