JEE Advanced · Physics · 17. Electrostatics
Paragraph:
The nuclear charge \((\mathrm{Ze})\) is non-uniformly distributed within a nucleus of radius \(R\). The charge density \(\rho(r)\) [charge per unit volume] is dependent only on the radial distance \(r\) from the centre of the nucleus as shown in figure. The electric field is only along the radial direction.

Question:
The electric field within the nucleus is generally observed to be linearly dependent on \(r\). This implies
- A \(a=0\)
- B \(a=\frac{R}{2}\)
- C \(a=R\)
- D \(a=\frac{2 R}{3}\)
Answer & Solution
Correct Answer
(C) \(a=R\)
Step-by-step Solution
Detailed explanation
In case of solid sphere of charge of uniform volume density.
\(
E=\frac{1}{4 \pi \varepsilon_0} \cdot \frac{q}{R^3} \cdot r \text { or } E \propto r
\)
Thus, for \(E\) to be linearly dependent on \(r\), volume charge density should be constant.
or \(\quad a=R\)
\(\therefore\) correct option is (c).

\(
E=\frac{1}{4 \pi \varepsilon_0} \cdot \frac{q}{R^3} \cdot r \text { or } E \propto r
\)
Thus, for \(E\) to be linearly dependent on \(r\), volume charge density should be constant.
or \(\quad a=R\)
\(\therefore\) correct option is (c).

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