Question

In the adjoining circuit of logic gate, the output Y becomes zero if the inputs are

A. $A = 1,B = 1,C = 0$
B. $A = 0,B = 0,C = 0$
C. $A = 0,B = 1,C = 1$
D. $A = 1,B = 0,C = 0$

Answer 1

The given circuit represents a logic gate. The first gate is an AND gate, the second gate is a NOT gate and the third gate is a NAND gate. The outputs of AND gate and NOT gate are again input to the NAND gate. A and B are the input to the AND gate and P is the output. C is the input to the NOT gate and Q is the output. Y is the output of the NAND gate.

Complete step by step solution:
Given,
The inputs to AND gate are A and B.
The input to the NOT gate is C.
The output of the NAND gate is Y.
The truth table of AND gate is,

The truth table of NOT gate,

The truth table of NAND gate,

From the truth table of the NAND gate, it can be observed that the output is zero when both the inputs P and Q is 1. Now the output P from AND gate will be 1 when input A and B is 1. Output Q from NOT gate will be 1 when input C is 0. Hence, when A and B is 1 and C is 0 then the output Y will be zero.

Hence, the correct answer is (A).

Note: The students have to apply the concept of logic gates and circuit. The truth table of each of AND gate, NOT gate, and NAND gate helps in obtaining the output of the combination of the gates. In order to get output 0, the inputs to the NAND gate has to be 1. For input as 1 to NAND gate, the output of AND gate has to be 1 and the output of NOT gate 1. Thus the input to AND gate is 1 and the input of NOT gate is 0.