2 Marks Question & Answers

2 MARKS QUESTIONS & ANSWERS

1. What is meant by signal and give its types?

A signal (voltage or current) is physical quantity that varies with time. A signal can be classified as analog and digital signal. A continuously varying signal is known as analog signal. Example: a sinusoidal voltage A signal which have only two discrete values is called as digital signal. Example: a square wave signal.

2. What is meant by digital circuit?

An electronic circuit that handles only a digital signal is referred to as digital circuit. The output voltage of a digital circuit is either low os high and no other value. In other words, digital operation has two states. They are expressed as (High or Low) or (ON or OFF) or (1 or 0).

3. What are AND Gate and give the truth table?

● AND Gate performs logical multiplication and it is known as the AND function. 

● The AND has two or more inputs and a single output. Logical AND operator is denoted by 'x' or '.'.

● A.B can be read as "A AND B" or "A times B".

4. What are OR Gate and give its truth table?

● The OR Gate performs logical addition and it is known as the OR operation.

● The OR Gate has two or more inputs and one output.

5. What are NOT Gate and give its truth table?

● NOT Gate performs a logic function which is inversion operation or "complement" operation. NOT gate has only one input and one output.

● When the input is low the output will be high. When the input is high the output will be low.

6. What are NAND gates and give their truth table?

NAND Gate is the inverted AND gate. It is a combination AND gate and NOT gate.

The NAND gate is a universal gate. Because its repeated use can produce all other logic gates such as AND, OR and NOT gates.

Symbol of NAND Gate

7. What are NOR Gate and give its truth table?

● NOR Gate is the inverted OR function. The output of NOR gate is high if all inputs are low. NOR Gate is a Universal Logic gate.

8. What are universal gates?

NAND & NOR gates are universal gates. Because using these 2 gates, we can produce all other logic gates such as AND, OR and NOT gates and all kinds of logical operation can be performed.

9. State Demorgan's theorem:

Demorgan suggested two theorems that form an important part of Boolean algebra

(AB)'=A'+B'

(A+B)'=A'.B'

(AB)'=A'+B': The complement of a product is equal to the product of the complements.

(A+B)'=A'.B': The complement of a sum is equal to the product of the complements.

10. Name the two canonical forms for Boolean algebra:

● Standard sop forms (sop)-sum of product

● Standard pos forms (pos) - product of sum.

11. Simplify the following boolean expression: ab'c'+ab'c+abc.

Given: ab'c'+ab'c+abc

ab'c'+ab'c+abc=ab'c'+ac(b'+b)

= ab'c'+ac

= a(b'c'+c)

= a(b'+c)

= ab'+ac

12. Simplify: x+x'y

Z = x + x'y = x + xy + x'y

= x + y(x + x')

Z = x + y

13. Two significant features of tabular method of minimization of Boolean function:

● It is an exact method to simplify the Boolean expression.

● It can be used to simplify expression with 7, 8 or even 10 variables.

14. What is meant by combinational circuit?

A combinational circuit is defined as a logic circuit the output of which depends only upon the combination of the inputs. The output does not depends on the past inputs or outputs. Thus combinational circuit do not have memory.

Examples: Adder, subtractors, multiplexers and comparators etc.,

15. What is meant by sequential circuit?

In case of a sequential circuit, the output of which depends upon the present time, the previous output and the sequence in which input are applied. Sequential circuit requires a memory element.

Examples: Flip-flops

16. Explain half adder with its truth table.

Half Adder is a combinational circuit that performs the addition of two bits. This circuit needs two binary inputs and two binary outputs. Then have two binary outputs as sum and carry.

17. What are full adder and draw logical circuit of full adder using 2 half adder?

● Full adder is a combinational circuit that forms the arithmetic sum of three input bits.

● It contains three inputs and two outputs (sum and carry).