A 2-input NOR gate has one input permanently connected to logic LOW (0). How does the output behave with respect to the other input?
Output is the complement of the other input
A NOR gate produces the logical OR of its inputs followed by inversion. For a 2-input NOR gate with inputs A and B the output is:
Output = NOT(A + B) = (A + B)'
Here one input is permanently tied to logic LOW (0). Substituting B = 0 and using the OR identity A + 0 = A:
Output = NOT(A + 0) = NOT(A) = Ā
So the gate simply inverts the remaining input. The verification table makes this clear:
| A | B = 0 | Output = (A + B)' |
|---|---|---|
| 0 | 0 | 1 |
| 1 | 0 | 0 |
When A = 0 the output is 1, and when A = 1 the output is 0 — the output is always the complement of the other input, which is the correct answer. This is a standard technique: a NOR gate with one input grounded behaves as a NOT (inverter) gate, just as a NAND gate with one input tied HIGH also acts as an inverter.
The output being always LOW would only occur if an input were held HIGH (since any HIGH input forces a NOR output to 0), not LOW. The output being always HIGH is impossible here because when A = 1 the sum is 1 and the inverted result is 0. And the output does not follow the other input directly — that describes a buffer, whereas the NOR here inverts the signal.
Important Questions from Logic Gates
A two-input logic gate is giving high output only when both the inputs are high. For all other input conditions, the output is low. Select the correct logic gate.
The output is high only if one of the input is high. The above statement represents _____
The number of gate inputs, required to realize expression ABC + AB̅CD + EF̅ + AD is
Which of the following is logically equivalent?
A. ¬p → (q → r) and q → (p ∨ r)
B. (p → q) → r and p → (q → r)
C. (p → q) → (r → s) and (p → r) → (q → s)
Choose the correct answer from the options given below :
Consider the expression Y = P ⨁ Q ⨁ R where P, Q, R are the input variables and Y is the output variable. Y will be logic 0 if
(A) an odd number of input variables are 1
(B) an even number of input variables are 1
(C) an odd number of inputs variables are 0
(D) an even number of input variable are 0
(E) an odd number of input variable between 0 and 1
Choose the correct answer from the options given below:
