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Saturday, 31 October

JEE Main 2021 · PhysicsMultiple choiceDiagram basedMediumData or graph

JEE Main 26 August 2021, Shift 1, Physics Q13

Question 13 of 90 in this shift, Physics question 13 of 30, Section A.

A solid metal sphere of radius R having charge q is enclosed inside the concentric spherical shell of inner radius a and outer radius b as shown in figure. The approximate variation electric field E⃗\vec{E} as a function of distance r from centre O is given by :

The figure, in words

Concentric circles: a hatched inner disc of radius R with centre O, a concentric ring region between circles of radius a and radius b; slanted lines are drawn across the outer ring region. Radii R, a and b are labelled.
  1. (1)[figure: graph of E vs r with R, a, b marked on the r-axis; curve rises from the origin up to a peak at r=R, then drops to zero; zero between R and b; at r=b a vertical jump to a peak, then a decaying curve for r>b]
  2. (2)[figure: graph of E vs r with R, a, b marked on the r-axis; zero up to r=b; at r=b a vertical jump to a peak, then a decaying curve for r>b]
  3. (3)[figure: graph of E vs r with R, a, b marked on the r-axis; zero up to r=R; at r=R a vertical jump to a peak, a decaying curve falling to near zero at about r=a; zero between a and b; at r=b a second vertical jump to a peak (same height as the first), then a decaying curve]Official answer
  4. (4)[figure: graph of E vs r with R, a, b marked on the r-axis; zero up to r=R; at r=R a vertical jump to a peak, then a single smoothly decaying curve continuing through a and b]

Official answer

Option 3

NTA final key.

Chapter
Electric Charges and Fields
Topic
Gauss's Law
Idea tested
Field of Concentric Conducting Shells

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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.