Question

NAND and NOR gates are called universal gates because they
A. are universally available
B. can be combined to produce OR, AND and NOT gates.
C. are widely used in the integrated circuits.
D. can be easily manufactured.

Answer 1

Hint: Here we will proceed by defining NAND and NOR gates. Then we will be discussing how NAND and NOR gates can combine to produce OR, AND and NOT gates and hence we will obtain the required answer.

Complete Step-by-Step solution:
NAND gate: NAND gate is a logic gate which produces an output which is false only if all its inputs are true; thus, its output is complement to that of an AND.
NOR gate: NOR gate is a logic gate that implements logical NOR – it behaves according to the truth table to the right. NOR is the result of the negation of the OR operator.
The NAND gate and the NOR gate can be said to be universal gates since combinations of them can be used to accomplish any of the basic operations and can thus produce an inverter, an OR gate or an AND gate. The non-inverting gates do not have this versatility since they can’t produce an invert.
NAND and NOR gates are universal gates because all the other gates can be created by using these gates.
Examples:
NOT as NOT this is made by joining the inputs of a NOR gate. As a NOR gate is equivalent to an OR gate leading to NOT gate, this automatically sees to the ‘OR’ part of the NOR gate, eliminating it from consideration and leaving only the NOT part.
NOR as OR the OR gate is simply a NOR gate followed by a NOT gate. NOR as AND an AND gate gives a 1 output when both inputs are 1; a NOR gate gives a 1 output only when both inputs are 0. Therefore, an AND gate is made by inverting the inputs to a NOR gate. NOR as NAND a NAND gate is made using an AND gate in series with a NOT gate.
Thus, the correct option is B. can be combined to produce OR, AND and NOT gates.

Note: The OR gate is a logic gate that implements logical disjunction – it behaves according to the adjacent truth table. The AND gate is a logic gate that implements logical conjugation – it behaves according to the truth table to the right. The NOT gate is a logic gate that produces an inverted version of the input as output.