JEE Main 2021 · 26 February · evening · Single correct · +4 / −1
Given below are two statements:
Statement I : An electric dipole is placed at the center of a hollow sphere. The flux of the electric field through the sphere is zero but the electric field is not zero anywhere in the sphere.
Statement II : If R is the radius of a solid metallic sphere and Q be the total charge on it. The electric field at any point on the spherical surface of radius r (< R) is zero but the electric flux passing through this closed spherical surface of radius r is not zero..
In the light of the above statements, choose the correct answer from the options given below :
- (a) Both Statement I and Statement II are true
- (b) Statement I is false but Statement II is true
- (c) Statement I is true but Statement II is false
- (d) Both Statement I and Statement II are false
Answer and solution
Answer (c) Statement I is true but Statement II is false
Solution
Physics sir · 3 steps
Flux sees only the enclosed charge, but the field feels every charge nearby.
- Statement I. The dipole has +q and -q inside the sphere, so q_(enc) = 0 and the flux q_(enc)/ε₀ is zero. The two charges still produce a field at every point, because their fields do not cancel exactly anywhere. Statement I is true.
∮ E⃗· dA⃗ = q_(enc)/ε₀
- Statement II. In a conductor, all of the charge Q sits on the outer surface at radius R. A sphere of radius r < R encloses no charge, so the flux through it is zero. The field inside the metal is also zero. Statement II claims the flux is not zero, so it is false.
- So. Statement I is true and Statement II is false, which is option (c).
The idea to keep. Gauss's law fixes the flux from the enclosed charge alone. Zero flux can come with a nonzero field (a dipole inside), and inside a conductor both the field and the flux are zero.
Answer from the NTA final answer key. Solution by PrepWiser.