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Saturday, 31 October

JEE Main 2020 · PhysicsMultiple choiceSingle correctMediumMulti-step

JEE Main 3 September 2020, Shift 1, Physics Q14

Question 14 of 75 in this shift, Physics question 14 of 25.

An elliptical loop having resistance R, of semi major axis a, and semi minor axis b is placed in a magnetic field as shown in the figure. If the loop is rotated about the xx-axis with angular frequency ω\omega, the average power loss in the loop due to Joule heating is :

The figure, in words

Axes drawn at left: z vertical, x to the right, y slanting down-left. At right: four parallel vertical arrows labelled B (pointing up) pass through a flat ellipse drawn in the horizontal plane; the ellipse has a semi-axis marked a along the x direction (x labelled at its right end) and a semi-axis marked b along the y direction (y labelled at the lower end).
  1. (1)π2a2b2B2ω22R\frac{\pi^2 a^2 b^2 B^2 \omega^2}{2R}Official answer
  2. (2)πabBωR\frac{\pi a b B \omega}{R}
  3. (3)π2a2b2B2ω2R\frac{\pi^2 a^2 b^2 B^2 \omega^2}{R}
  4. (4)zero

Official answer

Option 1

NTA final key (Sep 2020).

Chapter
Electromagnetic Induction
Topic
Faraday's Law
Idea tested
AC Generator Principle

Same idea in other shifts

Asked 5× in all
  1. 1 Feb 2024, Shift 2 · Q58A coil of 200 turns and area 0.20 m20.20\ \mathrm{m^2} is rotated at half a revolution per second and is placed in uniform magnetic field of…EasyNumerical value
  2. 24 Jun 2022, Shift 2 · Q58A circular coil of 1000 turns each with area 1m2^2 is rotated about its vertical diameter at the rate of one revolution per second in a…EasyNumerical value
  3. 26 Aug 2021, Shift 2 · Q28A circular coil of radius 8.0 cm and 20 turns is rotated about its vertical diameter with an angular speed of 50 rad s−1^{-1} in a uniform…EasyNumerical value
  4. 2 Sep 2020, Shift 1 · Q24A circular coil of radius 10 cm is placed in a uniform magnetic field of 3.0×10−53.0\times10^{-5} T with its plane perpendicular to the field…MediumNumerical 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.