NEET 2019 · PhysicsGauss spheresPrevious Year Question
A hollow metal sphere of radius R is uniformly charged. The electric field due to the sphere at a distance r from the centre
Answer: (B) is zero for r < R, decreases as r increases for r > R. Answer: (b) Solution: Apply Gauss's law to a charged hollow (shell) sphere.
- A.increases as r increases for r < R and for r > R
- B.is zero for r < R, decreases as r increases for r > R✓
- C.is zero for r < R, increases as r increases for r > R
- D.decreases as r increases for r < R and for r > R
Correct Answer
(B) is zero for r < R, decreases as r increases for r > R
Solution & Explanation
Answer: (b) Solution: Apply Gauss's law to a charged hollow (shell) sphere. Inside the shell (r < R): the Gaussian surface encloses no charge (all charge resides on the surface), so E = 0. Outside the shell (r > R): the entire charge Q acts as if concentrated at the centre, giving E = (1/4πε₀)·Q/r², i.e. E ∝ 1/r², which decreases as r increases. Hence: E = 0 for r < R and E decreases as r increases for r > R.
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