Current Electricity

JEE Main level, single correct, medium

229 of 380

Question 229 of 380

Water boils in an electric kettle in 20 minutes after being switched on. Using the same main supply, the length of the heating element should be _____ to _____ times of its initial length if the water is to be boiled in 15 minutes.

Show answer and solution

Answer: (A) decreased, 3/43 / 4

P=v2R,R=ρℓAP∝1ℓP1P2=t2t1=1520=ℓ2ℓ1ℓ2=34ℓ1\begin{aligned} & \mathrm{P}=\frac{\mathrm{v}^2}{\mathrm{R}}, \mathrm{R}=\frac{\rho \ell}{\mathrm{A}} \\ & \mathrm{P} \propto \frac{1}{\ell} \\ & \frac{\mathrm{P}_1}{\mathrm{P}_2}=\frac{\mathrm{t}_2}{\mathrm{t}_1}=\frac{15}{20}=\frac{\ell_2}{\ell_1} \\ & \ell_2=\frac{3}{4} \ell_1\end{aligned}

JEE Main question paper PDF

Open a shift to read the full paper on this page, or download it.

JEE Main 2025 Apr 2 Shift 1 question paper

Open Download PDF

Opening paper…

Explain it as a whiteboard videoStep-by-step, in Hinglish or English. Your first video needs no login.Solved it on paper but got it wrong?Upload a photo of your working. Mistake Doctor marks the exact line that broke.
See it move: Circuit builder simulationDrag the sliders and watch the numbers in this question change.Revise Current Electricity firstFormula sheet, solved examples and the traps students fall into.

More Physics practice

JEE Main Physics practice question on Current Electricity (Electric Power and Heating Effect of Current), with the answer and a step-by-step solution. Scan a question from your own book or paper to get a whiteboard video.