# MCQs on Digital Electronics

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01․ OR-AND realization of a combinational circuit is equivalent to
NAND-NOR realization
NAND-NAND realization
NOR-NAND realization
NOR-NOR realization

The NOR-NOR realization is equivalent to OR-AND realization. Bubbled inputs of AND gate will results a NOR gate and compliment of OR gate is a NOR gate. Therefore, NOR-NOR realization is equivalent to OR-AND realization and vice versa.

02․ For the design of a combinational circuit with four inputs using only NAND gates, the number of K-maps required for the simplification process is
0
1
2
4

K-maps are used for simplification of logical expression. These are more suitable up to 4 or 5 variables. Above 5 variables it is complicated to solve the logical expression. For four inputs, the number of k maps required for the simplification presses is 1.

03․ The AND-OR realization of a combinational circuit requires three 3-input AND gates and one 3-input OR gate. This circuit can be designed using
four input NAND gates only
three 3-input OR gates and one 3-input AND gate
three 3-input NAND gates and one 3-input NOR gate
none of the above

The NAND-NAND realization is equivalent to AND-OR realization. Bubbled inputs of OR gate will results a NAND gate and compliment of AND gate is a NAND gate. Therefore, NAND-NAND realization is equivalent to AND-OR realization and vice versa.

04․ Logic circuits are
analog circuits
digital circuits
hybrid circuits
none of these

A digital circuit is typically constructed from small electronic circuits called logic gates that can be used to create combinational logic. Each logic gate is designed to perform a function of boolean logic when acting on logic signals.

05․ Switching circuits are
analog circuits
digital circuits
hybrid circuits
none of these

Switching circuits are mainly digital circuits. By using of different gates we can get the required outputs. For example EX-OR or EX-NOR gates are used as stair case switches.

06․ The devices commonly used for making digital circuits are
mechanical switches
relays
contact switches
semiconductor devices

A digital circuit is typically constructed from small electronic circuits called logic gates that can be used to create combinational logic. Each logic gate is designed to perform a function of boolean logic when acting on logic signals. A logic gate is generally created from one or more electrically controlled switches, usually transistors but thermionic valves have seen historic use.

07․ The voltages corresponding to LOW and HIGH levels respectively are given below. Identify the voltages which correspond to positive logic system.
0 V and 5 V
–1.5 V and – 5 V
5 V and 0 V
1 V and -5 V

Duel expression is used to convert positive logic to negative logic or vice versa. For positive logic, Logic '0' = 0 V logic '1' = 5 V From the above statement we can say that logic '0' value is smaller than logic '1' for positive logic systems.

08․ The voltages corresponding to LOW and HIGH levels respectively are given below. Identify the voltages which correspond to negative logic system.
0 V and 5 V
–1.5 V and – 0.5 V
5 V and 0 V
1 V and 5 V

Duel expression is used to convert positive logic to negative logic or vice versa. For negative logic, Logic '0' = 5 V logic '1' = 0 V From the above statement we can say that logic '0' value is higher than logic '1' for negative logic systems.

09․ The voltage levels for positive logic system
must necessarily be positive
must necessarily be negative
may be positive or negative
must necessarily be 0 V and 5 V

For positive logic, Logic '0' = 0 V logic '1' = 5 V From the above statement we can say that logic '0' value is smaller than logic '1' for positive logic systems. It may be negative or positive, but logic '1' value should be more than logic '0' value.

10․ The voltage levels for negative logic system
must necessarily be negative
may be negative or positive
must necessarily be positive
must necessarily be 0 V and –5 V

For negative logic, Logic '0' = 5 V logic '1' = 0 V From the above statement we can say that logic '0' value is higher than logic '1' for negative logic systems. It may be positive or negative, but logic '0' value should be more than logic '1'.

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