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An insulating solid sphere of radius R h...

An insulating solid sphere of radius R has a uniformly positive charge density `rho`. As a result of this uniform charge distribution there is a finite value of electric potential at the centre of the sphere, at the surface of the sphere and also at a point out side the sphere. The electric potential at infinity is zero.
Statement-1: When a charge 'q' is taken from the centre to the surface of the sphere, its potential energy changes by `(qrho)/(3 in_(0))`
Statement-2 : The electric field at a distance `r (r lt R)` from the centre of the the sphere is `(rho r)/(3in_(0))`

A

Both Statement-1 & Statement-2 are correct & Statement-2 is the correct explanation of Statement-1

B

Both Statement-1 & Statement-2 are correct & Statement-2 is not the correct explanation of Statement-1

C

Statement - 1 is correct but Statement -2 is incorrect

D

Statement-2 is correct but Statement-1 is incorrect

Text Solution

AI Generated Solution

The correct Answer is:
To solve the problem, we will analyze both statements provided and derive the necessary equations step by step. ### Step 1: Electric Field Inside the Sphere For a uniformly charged insulating solid sphere of radius \( R \) with a uniform charge density \( \rho \), we can use Gauss's Law to find the electric field inside the sphere at a distance \( r \) from the center (where \( r < R \)). Using Gauss's Law: \[ \oint \mathbf{E} \cdot d\mathbf{A} = \frac{Q_{\text{enc}}}{\epsilon_0} \] Where \( Q_{\text{enc}} \) is the charge enclosed by the Gaussian surface. The charge enclosed within a radius \( r \) is given by: \[ Q_{\text{enc}} = \rho \cdot \text{Volume} = \rho \cdot \frac{4}{3} \pi r^3 \] The area \( A \) of the Gaussian surface (a sphere of radius \( r \)) is: \[ A = 4 \pi r^2 \] Substituting into Gauss's Law: \[ E \cdot 4 \pi r^2 = \frac{\rho \cdot \frac{4}{3} \pi r^3}{\epsilon_0} \] Solving for \( E \): \[ E = \frac{\rho r}{3 \epsilon_0} \] ### Step 2: Change in Potential Energy To find the change in potential energy when moving a charge \( q \) from the center of the sphere to the surface, we need to calculate the potential difference \( V \) between these two points. The electric potential \( V \) at a distance \( r \) from the center is given by: \[ V = -\int E \, dr \] The potential at the center (where \( r = 0 \)) is: \[ V(0) = 0 \quad \text{(arbitrarily chosen as reference)} \] The potential at the surface \( V(R) \) can be calculated as: \[ V(R) = -\int_0^R \frac{\rho r}{3 \epsilon_0} \, dr \] Calculating the integral: \[ V(R) = -\left[ \frac{\rho}{3 \epsilon_0} \cdot \frac{r^2}{2} \right]_0^R = -\frac{\rho R^2}{6 \epsilon_0} \] The change in potential energy \( \Delta U \) when moving charge \( q \) from the center to the surface is: \[ \Delta U = q \cdot (V(R) - V(0)) = q \cdot \left(-\frac{\rho R^2}{6 \epsilon_0} - 0\right) = -\frac{q \rho R^2}{6 \epsilon_0} \] ### Step 3: Analyzing the Statements 1. **Statement 1**: The change in potential energy when a charge \( q \) is taken from the center to the surface is given as \( \frac{q \rho}{3 \epsilon_0} \). Our calculation shows it is \( -\frac{q \rho R^2}{6 \epsilon_0} \). Therefore, **Statement 1 is false**. 2. **Statement 2**: The electric field at a distance \( r < R \) is given as \( \frac{\rho r}{3 \epsilon_0} \). Our calculation confirms this is true. Therefore, **Statement 2 is true**. ### Conclusion - **Statement 1**: False - **Statement 2**: True ### Final Answer The correct option is that Statement 2 is correct and Statement 1 is incorrect. ---

To solve the problem, we will analyze both statements provided and derive the necessary equations step by step. ### Step 1: Electric Field Inside the Sphere For a uniformly charged insulating solid sphere of radius \( R \) with a uniform charge density \( \rho \), we can use Gauss's Law to find the electric field inside the sphere at a distance \( r \) from the center (where \( r < R \)). Using Gauss's Law: \[ \oint \mathbf{E} \cdot d\mathbf{A} = \frac{Q_{\text{enc}}}{\epsilon_0} ...
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