MCQEasyJEE 2023Electric Potential & Potential Energy

JEE Physics 2023 Question with Solution

For a uniformly charged thin spherical shell, the electric potential (VV) radially away from the center of the shell can be graphically represented as:

A thin spherical shell with center O and a radius marked from O to point A on the surface, labeled R.
  • A
    Graph of electric potential V versus radial distance r showing constant potential up to r = R, then decreasing linearly beyond R.
  • B
    Graph of electric potential V versus radial distance r rising linearly from the origin up to r = R, then decreasing along a curved path.
  • C
    Graph of electric potential V versus radial distance r increasing nonlinearly up to r = R, then decreasing linearly beyond R.
  • D
    Graph of electric potential V versus radial distance r remaining constant from the center to r = R, then decreasing nonlinearly for r greater than R.

Answer

Correct answer:D

Step-by-step solution

Standard Method

Given: A uniformly charged thin spherical shell.

Find: The graph of electric potential VV as a function of radial distance rr from the center.

For a thin spherical shell, the electric potential is constant everywhere inside the shell:

V=KQRV = \frac{KQ}{R}

for rRr \le R.

Outside the shell, the potential is the same as that due to a point charge placed at the center:

V=KQrV = \frac{KQ}{r}

for r>Rr > R.

So, from the center up to r=Rr = R, the graph is a horizontal line. Beyond r=Rr = R, the potential decreases with rr following an inverse relation.

Therefore, the correct option is D.

Common mistakes

  • Assuming the potential inside the shell is zero because the electric field inside is zero. This is incorrect because zero electric field means the potential is constant, not necessarily zero. Use V=KQRV = \frac{KQ}{R} for all rRr \le R.

  • Confusing the shell with a solid uniformly charged sphere. For a solid sphere, the potential inside varies with rr, but for a thin spherical shell it remains constant inside. Identify the charge distribution before choosing the graph.

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