Question

The logic gate represented in given figure is

A) OR Gate
B) NOT Gate
C) NAND Gate
D) XOR Gate

Answer 1

Hint: The given figure is divided into two sections. Truth table of each section is written down separately to determine the output of the given figure, easily. From the figure, it is clear that two NOR gates are used. NOR gate is logically equivalent to an inverted OR gate.

Complete step by step answer:
Logic gates are electronic devices which perform Boolean algebra. Logic gates work on one or more binary inputs to produce a single output. By binary inputs, we mean two inputs: 1 for positive and 0 for negative. It is clear from the given figure that A and B are the two binary inputs of the combination of gates and Y is the output of the combination. We are required to determine the equivalent logic gate of the given combination of gates. For this, let us separate the combination into two. Clearly, the combination is made up of two NOR gates. Therefore, on separating the combination, we get two NOR Gates: the first one being fed with two binary inputs and the second one being fed with two binary inputs, separated from the single output of the first NOR gate, as shown in the following diagram. Let us call the output of the first NOR gate as X. Also, let us call the inputs of the second NOR gate, R and S. Output of the second NOR gate is nothing but the final output of the given combination of gates. Hence, let us call the output of the second gate, Y itself.

The truth table of the first NOR Gate is given as follows.

A	B	X
0	0	1
0	1	0
1	0	0
1	1	0

Here, A and B are the two binary inputs and Y is the output of the first NOR gate. Outputs of different combinations of inputs are noted down in the truth table. Clearly, this truth table looks like the truth table of an inverted OR gate. Hence, we can conclude that a NOR gate acts as an inverted OR gate.
Now, at the junction where the first NOR gate and the second NOR gate meet, the single binary output of the first NOR gate (X) separates itself and sends the same signals to both the input channels of the second NOR gate (R and S), as shown in the following-

The truth table of the second NOR gate is given by

R	S	Y
1	1	0
0	0	1
0	0	1
0	0	1

Here, R and S are the inputs of the second NOR gate. Both these binary input signals are the same as the output signal of the first NOR Gate (X). Also, output of the second NOR gate is given by Y, which is nothing but the output of the given combination of gates.
Now, let us cross check this truth table with the truth tables of logic gates provided in the options. Clearly, output of the combination is equal to the output of an OR gate. Also, using the concept of NOR gate as an inverted OR gate here, in this case, the second NOR gate acts as an inverted OR gate of the first NOR gate, which is already an inverted OR Gate. Since inversion nullifies the inversion, the equivalent gate of the given combination of two NOR gates is nothing but an OR gate, as shown below.

Therefore, the correct answer is option A.

Note:
A NOR gate is also similar to a NOT gate. At the same time, when we use a combination of three NOR gates, in such a way that outputs of the first two NOR gates are fed as the inputs of the third NOR gate, the equivalent gate of the combination is nothing but an AND gate. It is for this reason that NOR gates are also called Universal gates.