Question

The output of an AND gate is connected to both the inputs of NOR gate, then this circuit will act as a
(A) OR gate
(B) NOR gate
(C ) AND gate
(D) NOT gate
(E) NAND gate

Answer 1

Hint: All other digital circuits are made up of these three basic logic gates. Hence, NOR gate can be made of OR and NOT gate. In other words, output of OR gate is connected to the input of NOT gate. Thus the output of NOR gate is opposite to OR gate. An OR gate is a logic circuit that has two or more inputs but only one output. The output of an OR gate is high, if any or all the inputs are high. Hence, the output of NOR gate will be the opposite of OR gate.

Complete answer:
 A logic gate is a digital circuit with one or input signal but only one output signal. There are three basic logic gates. All digital circuits are made with these three gates. That is, AND gate, OR gate and NOT gate.
An OR gate is a logic circuit that has two or more inputs but only one output. The output of an OR gate is high, if any or all the inputs are high. Similarly, AND gate is a logic circuit that has two or more inputs and one output. NOR gate can be made of OR and NOT gate. In other words, output of OR gate is connected to the input of NOT gate. Thus the output of NOR gate is opposite to OR gate. When the two outputs of NOR gate are joined together, it acts as a NOT gate.

The Boolean expression of AND gate is,
 $Y=A.B$ where, Y is the output.
The Boolean expression for NOR gate is,
$Y=\overline{A+B}$ where, Y is the output.
Thus the output of AND gate is AB. Since the two outputs of NOR gate are joined together, it acts as a NOT gate.
Then the resultant output is,
$Y=\overline{A.B}$
Therefore, the given circuit acts as a NAND gate.

So, the correct answer is “Option E”.

Note:
Thus the output of NOR gate is opposite to OR gate. An OR gate is a logic circuit that has two or more inputs but only one output. The output of an OR gate is high, if any or all the inputs are high. Hence, the output of NOR gate will be the opposite of OR gate. When the two outputs of NOR gate are joined together, it acts as a NOT gate.