CBSE Class 12 Physics Current Electricity Solved Examples

CBSE Class 12 Physics Current Electricity Solved Examples. Please refer to the examination notes which you can use for preparing and revising for exams. These notes will help you to revise the concepts quickly and get good marks.

Ex. 1 A cylindrical wire is stretched to increase its length by 10%. The percentage increase in the resistance of the wire will be–
(A) 20% (B) 21% (C) 22% (D) 24%

Ex. 2 The equivalent resistance between A and B
is–

(A) 2R/3 (B) R/3 (C) R (D) 3R

Sol. (A)The circuit is equivalent to Fig. It is a balanced wheatstone bridge between abcd, and then in parallel (2R) resistances. Thus ignoring resistance between bd arm. The circuit is equivalent to three (2R) resistances in parallel
(abc, adc, aRRc).

Ex. 3 In the adjoining network of resistors, each is of resistance r ohm, the equivalent resistance
between points A and B is–

Imagine, A being pulled on the left side, then abcd becomes a balanced wheatstone bridge Fig. The arm bd can be ignored. Then resistance between A, B becomes = .i.e.1/R_eq=1/2r /+1/2r=1/r =  R_eq =r

Ex. 6 Fig. represents a balanced Wheatstone's Bridge. The value of resistance R will be–

Ex. 7 An electric current of 5 amp. is divided in three branches forming a parallel combination. The length of the wire in the three branches are in the ratio, 2, 3 and 4 ; their diameters are in the ratio 3, 4 and 5. Find the currents in each branch if the wire are of the same material.
Sol Let the length of three wires be 2l, 3l and 4l respectively and their radii be 3r, 4r and 5r respectively. If S be the specific resistance,then

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