CBSE Guess > Papers > Important Questions > Class XII > 2012 > Computer Science > Computer Science Mr. Pradumna Singh

Computer Science- CBSE CLASS XII

Q. 21. State and verify Absorption law in Boolean algebra.                             For - 2 Marks

Ans.: Absorption law states that :
a) x+xy=x                    b) x(x+y)=x
Verification:
x+xy=x
LHS=x+xy     by distributive law
=x(1+y)  since 1+y=1
=x.1       since 1.x=x
=x = RHS, hence verified

OR (using truth table)

Here column x and x+xy are identical, hence proved.

Q. 22. Write the SOP form of a Boolean function G, which is represented in a truth table as follows :                             For - 2 Marks

Ans. Add extra column for min term and write min terms for the rows which have output (G) as 1:-

Now sum all the min terms to get the SOP as:

Therefore SOP of F(A,B,C)= A’B’C’+A’B’C+AB’C’+ABC

Q. 23. Write the equivalent Boolean Expression R for the following circuit diagram :                             For - 1 Marks

Ans. : (A+B) (A+B’) (A’+B)

Q. 24. If F(P,Q,R,S) = π (0,2,4,5,6,7,8,10,11,12,14) , obtain the simplified form using K-Map.                                  For - 4 Marks

Ans. Draw the 4 variable K-Map, plot & group the 0s starting from bigger to smaller group:

Reducing:
Octet = M0.M2.M4.M6.M8.M10.M12.M14
          = S
Quad = M4.M5.M6.M7
          = P+Q’
Pair    = M10.M11
          = P’+Q+R’

Therefore POS of F(P,Q,R,S)= S.(P+Q’).(P’+Q+R’)

Prepared By: Mr. Pradumna Singh
mail to: [email protected]