Question

Assertion :When current through a bulb decreases by 0.5%, the glow of bulb decreases by 1%. Reason: Glow (Power) which is directly proportional to square of current.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Assertion is incorrect but Reason is incorrect

Answer 1

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion

Power, $P=I^{2}R$

so,$\frac{P_f}{P_i}=\frac{I_f^2}{I_i^2}$

here, $I_f=I_i-I_i\left(0.5/100\right)=0.995I_i$

or $\frac{I_f}{I_i}=0.995$

thus, $\frac{P_f}{P_i}=(0.995{)}^2=0.99$

Decreases power $=\frac{P_i-P_f}{P_i}\times 100=[1-\frac{P_f}{P_i}]100=[1-0.99]100=1$%