Question

7.
If the resistance of a circuit is increased by 20%, then
approximately by what percent the current will reduce if
the supply voltage remains same ?
যদি এটা বৰ্ত্তনীৰ ৰােধ 20% বৃদ্ধি হয়, তেন্তে ইয়াৰ প্ৰৱাহ কিমান
শতাংশ কমিৰ যদি ইয়াৰ যােগান ধৰা বিভৱ একে থাকে?
যদি একটি বর্তনীর রােধ 20% বৃদ্ধি করা হয় তবে ইহার প্রবাহ
আনুমাণিক কত শতাংশ কমিবে, যদি ইহার যােগান ধরা বিভৰ একই
থাকে ?
(A) 17 %
(B) 80 %
Cy0.05 %
(D) 5 %​

Answer 1

Given info : If the resistance of a circuit is increased by 20%.

To find : approximately by what percentage of current will be reduce if the supply voltage remains same ?

solution : let resistance of a circuit is R.

if the resistance of the circuit is increased by 20% , new resistance of the circuit = R + 20% of R

= R + R/5 = 6R/5

let the supplied voltage is V.

from Ohm's law,

V = iR ⇒i = V/R [initial value of current ]

V = i' × (6R/5) ⇒ i' = 5V/6R [ final value of current ]

now percentage change in current = (i' - i)/i × 100

= (5V/6R - V/R)/(V/R) × 100

= -100/6

= -16.67 ≈ -17 % [ here negative sign indicates current is reduced by 17% ].

Therefore the correct option is (A)