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Saturday, 31 October

JEE Main 2020 · PhysicsMultiple choiceOtherHardMulti-step

JEE Main 9 January 2020, Shift 1, Physics Q13

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

A charged particle of mass 'm' and charge 'q' moving under the influence of uniform electric field Ei→\overrightarrow{E i} and a uniform magnetic field Bk→\overrightarrow{B k} follows a trajectory from point P to Q as shown in figure. The velocities at P and Q are respectively, vi→\overrightarrow{v i} and −2vj→-2\overrightarrow{v j}. Then which of the following statements (A, B, C, D) are the correct ? (Trajectory shown is schematic and not to scale) (A) E=34(mv2qa)E = \frac{3}{4}\left(\frac{mv^{2}}{qa}\right) (B) Rate of work done by the electric field at P is 34(mv3a)\frac{3}{4}\left(\frac{mv^{3}}{a}\right) (C) Rate of work done by both the fields at Q is zero (D) The difference between the magnitude of angular momentum of the particle at P and Q is 2 mav.

The figure, in words

Axes Y (vertical) and X (horizontal) meeting at O. Point P is on the Y axis at height a above O (vertical double-headed arrow labelled a between O and P, small right-angle mark at P). A horizontal line from P to the right with an arrow labelled v, which then curves downward and runs vertically down to point Q on the X axis (small right-angle mark at Q); O to Q is marked by a double-headed arrow labelled 2a. At Q a downward arrow is labelled 2v. The label E with an arrow above it is printed above the right part of the path, and B is printed with a circle containing a dot (symbol for field pointing out of the page) to its left.
  1. (1)(A), (B), (C), (D)
  2. (2)(B), (C), (D)
  3. (3)(A), (C), (D)
  4. (4)(A), (B), (C)Official answer

Official answer

Option 4

NTA final key (Jan 2020).

Chapter
Moving Charges and Magnetism
Topic
Lorentz Force
Idea tested
Work-Energy Theorem in Combined E and B Fields

Same topic in other shifts

All Lorentz Force questions
  1. 2 Apr 2026, Shift 1 · Q481 μ1\ \muC charge moving with velocity v⃗=(i^−2j^+3k^)\vec v=\left(\hat i-2\hat j+3\hat k\right) m/s in the region of magnetic field…EasyNumerical value
  2. 2 Apr 2026, Shift 2 · Q29A particle having charge 10−910^{-9} C moving in xx-yy plane in fields of 0.4j^0.4\hat{j} N/C and 4×10−3k^4 \times 10^{-3}\hat{k} T experiences a…MediumSingle correct
  3. 5 Apr 2026, Shift 1 · Q49The charged particle moving in a uniform magnetic field of (3i^+2j^) T(3\hat{i} + 2\hat{j})\,\mathrm{T} has an acceleration…MediumNumerical value
  4. 5 Apr 2026, Shift 2 · Q38A particle of charge qq and mass mm is projected from origin with an initial velocity…MediumSingle correct
  5. 8 Apr 2026, Shift 2 · Q48A 5 mg particle carrying a charge of 5π×10−65\pi \times 10^{-6} C is moving with velocity of (3i^+2k^)×10−2\left(3\hat{i} + 2\hat{k}\right) \times 10^{-2}…MediumNumerical value
  6. 3 Apr 2025, Shift 2 · Q40Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R Assertion A : If Oxygen ion…MediumAssertion–reason

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.