# MCQs on Digital Electronics

##### Page 27 of 35. Go to page 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35
01․ The output of a logic gate is 0 when all its inputs are at logic 1. The gate is either
a NAND or an AND
a NAND or an X-OR
a NOR or an X-NOR
a NAND or an X-NOR

The output of NAND gate is low when all inputs are high and the output of X-OR gate is low when all the inputs are same, either logic ‘0’ or logic ‘1’.

02․ The output of a logic gate is 0 when all its inputs are at logic 0. The gate is either
an AND or a NOR
a NAND or an X-OR
an OR or an X-OR
an OR or an X-NOR

The output of OR gate is low when all inputs are low and the output of X-OR gate is low when all the inputs are same, either logic ‘0’ or logic ‘1’.

03․ The number of rows in the truth table of a 4-input gate is
4
8
12
16

The number of rows in truth table indicates the number of outputs for given inputs. Therefore, the number of rows in the truth table of a 4-input gate is 16 (24 = 16).

04․ Which of the following statements is true?
OR and NOT gates are necessary and sufficient for realization of any logic function.
AND and NOT gates are necessary and sufficient for realization of any logic function.
NAND gates are not sufficient to realize any logic function.
NOR gates are sufficient to realize any logic function.

NAND and NOR gates are universal gates. We can implement any gate by using either NAND or NOR gate. Therefore, NOR gates or NAND gates are sufficient to realize any logic function.

05․ The output of a logic gate is 0 when all its inputs are at logic 0. The gate is either
an AND or a NOR
a NAND or an X-OR
an OR or an X-OR
an OR or an X-NOR

The output of OR gate is low when all inputs are low and the output of X-OR gate is low when all the inputs are same, either logic ‘0’ or logic ‘1’. Therefore, the output of a logic gate is 0 when all its inputs are at logic 0, then the gate is either an OR or an X-OR.

06․ The number of rows in the truth table of a 4-input gate is
4
8
12
16

The number of rows in truth table indicates the number of outputs for given inputs. Therefore, the number of rows in the truth table of a 4-input gate is 16 (24 = 16).

07․ Which of the following statements is true?
OR and NOT gates are necessary and sufficient for realization of any logic function.
AND and NOT gates are necessary and sufficient for realization of any logic function.
NAND gates are not sufficient to realize any logic function.
NOR gates are sufficient to realize any logic function.

NAND and NOR gates are universal gates. We can implement any gate by using either NAND or NOR gate. Therefore, NOR gates or NAND gates are sufficient to realize any logic function.

08․ For checking the parity of a digital word, it is preferable to use
AND gates
NAND gates
X-OR gates
NOR gates

The parity of a digital word is representing in flag register. The parity bit in a flag register is logic’1’, when the output contains even number of logic 1’s and the parity bit in a flag register is logic’0’, when the output contains odd number of logic 1’s. To check this condition X-OR gates are preferable.

09․ The most suitable gate to check whether the number of 1s in a digital word is even or odd is
X-OR
NAND
NOR
AND, OR, and NOT

To check the number of 1’s in digital word parity bit is used. The parity of a digital word is representing in flag register. The parity bit in a flag register is logic’1’, when the output contains even number of logic 1’s and the parity bit in a flag register is logic’0’, when the output contains odd number of logic 1’s. To check this condition X-OR gates are preferable.

10․ Which of the following operations is commutative but not associative?
AND
OR
X-OR
NAND

Let A, B and C are inputs, AND gate: 1. AB = BA, therefore it is following cumulative law. 2.f ABC = (AB)C = (AC)B = (BC)A, therefore it is following associative law. OR gate: 1. A+B = B + A, therefore it is following cumulative law. 2. A + B + C = (A + B) + C = (A+C) +B = (B + c) + A, therefore it is following associative law. In similar way X-Or gate will follow the both laws. NAND, NOR and X-NOR will follow only cumulative law but not follow the associative law.

<<<2526272829>>>