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Saturday, 31 October

JEE Main 2021 · PhysicsMultiple choiceDiagram basedMediumMulti-step

JEE Main 17 March 2021, Shift 2, Physics Q2

Question 2 of 90 in this shift, Physics question 2 of 30, Section A.

Two cells of emf 2E and E with internal resistance r1\mathrm{r_1} and r2\mathrm{r_2} respectively are connected in series to an external resistor R (see figure). The value of R, at which the potential difference across the terminals of the first cell becomes zero is

The figure, in words

Circuit: a rectangular loop with two cells in series on the top side, the left cell labelled 2E and the right cell labelled E, and a resistor labelled R on the bottom side.
  1. (1)r12−r2\frac{\mathrm{r_1}}{2}-\mathrm{r_2}Official answer
  2. (2)r12+r2\frac{\mathrm{r_1}}{2}+\mathrm{r_2}
  3. (3)r1−r2\mathrm{r_1}-\mathrm{r_2}
  4. (4)r1+r2\mathrm{r_1}+\mathrm{r_2}

Official answer

Option 1

NTA final key.

Chapter
Current Electricity
Topic
Kirchhoff's Laws
Idea tested
Cell EMF and Internal Resistance

Same idea in other shifts

Asked 10× in all
  1. 5 Apr 2026, Shift 2 · Q49When an external resistance of 5 Ω\Omega is connected across terminals of a cell, a current of 0.25 A flows through it. When the 5…EasyNumerical value
  2. 8 Apr 2024, Shift 1 · Q40In the given circuit, the terminal potential difference of the cell is :EasySingle correctHas a figure
  3. 31 Jan 2024, Shift 2 · Q56In the following circuit, the battery has an emf of 2V and an internal resistance of 23Ω\frac{2}{3}\Omega. The power consumption in the…MediumNumerical valueHas a figure
  4. 11 Apr 2023, Shift 2 · Q59Two identical cells each of emf 1.5 V1.5\ \mathrm{V} are connected in series across a 10 Ω10\ \Omega resistance. An ideal voltmeter connected…MediumNumerical value
  5. 27 Jul 2022, Shift 1 · Q41Two sources of equal emfs are connected in series. This combination is connected to an external resistance R. The internal resistances of…MediumSingle correct
  6. 30 Jul 2022, Shift 2 · Q24A cell sends a current through a resistance 4 Ω for time t and sends current through another resistance 16 Ω for the same time t.If the…MediumNumerical value
  7. 27 Aug 2021, Shift 1 · Q26First, a set of n equal resistors of 10 Ω\Omega each are connected in series to a battery of emf 20 V and internal resistance 10…MediumNumerical value
  8. 22 Jul 2021, Shift 2 · Q27In an electric circuit, a cell of certain emf provides a potential difference of 1.25 V across a load resistance of 5 Ω\Omega. However,…EasyNumerical value

Question text from the official JEE Main paper published by NTA; answer from the final answer key. Chapter, topic and idea tags, difficulty and skill are Lumi’s. This question needs a figure we do not reproduce; it is described in words above. Lumi analyses 108 of the 174 JEE Main shifts held from 2017 to 2026.