Logic Gates MCQs

Question 1

A logic probe is placed on the output of a gate and the display indicator is dim. A pulser is used on each of the input terminals, but the output indication does not change. What is wrong?

Accepted Answer

The output of the gate appears to be open.

Answer

The dim indication on the logic probe indicates that the supply voltage is probably low.

Answer

The dim indication is the result of a bad ground connection on the logic probe.

Answer

The gate is a tristate device.

Question 2

What is the Boolean expression for a three-input AND gate?

Accepted Answer

X = A · B · C

Answer

X = A + B + C

Answer

A – B – C

Answer

A $ B $ C

Question 3

Which of the following gates has the exact inverse output of the OR gate for all possible input combinations?

Accepted Answer

NOR

Answer

NOT

Answer

NAND

Answer

AND

Question 4

What is the difference between a 7400 and a 7411 IC?

Accepted Answer

7400 has four two-input NAND gates; 7411 has three three-input AND gates

Answer

7400 has two four-input NAND gates; 7411 has three three-input AND gates

Answer

7400 has two four-input AND gates; 7411 has three three-input NAND gates

Answer

7400 has four two-input AND gates; 7411 has three three-input NAND gates

Question 5

The output of an exclusive-OR gate is HIGH if ________.

Accepted Answer

the inputs are unequal

Answer

all inputs are LOW

Answer

all inputs are LOW

Answer

none of the above

Question 6

A clock signal with a period of 1 s is applied to the input of an enable gate. The output must contain six pulses. How long must the enable pulse be active?

Accepted Answer

Enable must be active for 6 s.

Answer

Enable must be active for 0 s.

Answer

Enable must be active for 3 s.

Answer

Enable must be active for 12 s.

Question 7

The AND function can be used to ________ and the OR function can be used to ________ .

Accepted Answer

enable or disable, enable or disable

Answer

enable, disable

Answer

disable, enable

Answer

detect, invert

Question 8

One advantage TTL has over CMOS is that TTL is ________.

Accepted Answer

not sensitive to electrostatic discharge

Answer

less expensive

Answer

faster

Answer

more widely available

Question 9

A 2-input NOR gate is equivalent to a ________.

Accepted Answer

negative-AND gate

Answer

negative-OR gate

Answer

negative-NAND gate

Answer

none of the above