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Saturday, 31 October

JEE Main 2020 · PhysicsMultiple choiceDiagram basedMediumCalculation

JEE Main 4 September 2020, Shift 1, Physics Q13

Question 13 of 75 in this shift, Physics question 13 of 25.

A wire A, bent in the shape of an arc of a circle, carrying a current of 2 A and having radius 2 cm and another wire B, also bent in the shape of arc of a circle, carrying a current of 3 A and having radius of 4 cm, are placed as shown in the figure. The ratio of the magnetic fields due to the wires A and B at the common centre O is :

The figure, in words

Two concentric circular arcs about a common centre O (marked with a dot): a smaller arc labelled A and a larger arc labelled B, each with an arrowhead showing current direction. Both arcs are open at the bottom, with two straight radial lines from O going down to the arcs' ends; angles 60° and 90° are marked near these lines at the bottom (60° at lower left, 90° at lower right).
  1. (1)6 : 5Official answer
  2. (2)2 : 5
  3. (3)4 : 6
  4. (4)6 : 4

Official answer

Option 1

NTA final key (Sep 2020).

Chapter
Moving Charges and Magnetism
Topic
Biot-Savart Law
Idea tested
Field at center of circular arc

Same idea in other shifts

Asked 8× in all
  1. 3 Apr 2025, Shift 1 · Q48A loop ABCDA, carrying current I=12\mathrm{I} = 12 A, is placed in a plane, consists of two semi-circular segments of radius…MediumNumerical valueHas a figure
  2. 30 Jan 2024, Shift 1 · Q42Two insulated circular loop A and B of radius 'a' carrying a current of 'I' in the anti clockwise direction as shown in the figure. The…MediumDiagram basedHas a figure
  3. 31 Jan 2024, Shift 2 · Q57Two circular coils PP and QQ of 100 turns each have same radius of π\pi cm. The currents in PP and RR are 1A1A and 2A2A respectively.…MediumNumerical value
  4. 10 Apr 2023, Shift 2 · Q59A straight wire carrying a current of 14 A is bent into a semicircular arc of radius 2.2 cm as shown in the figure. The magnetic field…MediumNumerical valueHas a figure
  5. 26 Jul 2022, Shift 1 · Q39BXB_X and BYB_Y are the magnetic fields at the centre of two coils X and Y respectively each carrying equal current. If coil X has 200…EasySingle correct
  6. 30 Jul 2022, Shift 2 · Q16In the following loop, magnitude of the magnetic field produced at the centre (O) of the loop is : (Assume AB and CD are infinitely…MediumSingle correctHas a figure
  7. 3 Aug 2021, Shift 1 · Q13A current I enters a circular coil of radius R, branches into two parts at A and then recombines at B (as shown in figure). The resultant…MediumDiagram basedHas a figure

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.