A sphere of radius \(R\) carries a nonuniform but spherically symmetric volume charge density that results in an electric field in the sphere given by \(\vec{E}=E_{0}(r / R)^{2} \hat{r},\) where \(E_{0}\) is a constant. Find the potential difference from the sphere's surface to its center.

Short Answer

Expert verified
The potential difference from the sphere's surface to its center is \(\frac{1}{3} E_{0} R\).

Step by step solution

01

Write down the formula for voltage

Potential difference, \(V\), is given by the negative integral of the electric field over a path: \(V = - \int_{a}^{b} \vec{E} \cdot d\vec{l}\), where \(a\) is the starting point, \(b\) is the ending point, and \(d\vec{l}\) is the infinitesimal path element. In this problem, we want to find the potential difference from the sphere's surface, \(R\), to its center, \(0\).
02

Set up the path integral

Since the electric field is directed radially (\(\hat{r}\)) and the path from the sphere's surface to the center is also radial, \(d\vec{l} = -dr\hat{r}\), gives a scalar equation: \(V = - \int_{R}^{0} E_{0}(r / R)^{2} (-dr)\). The extra negative sign is because the path is from the surface to the center. It comes from that the element \(dr\) goes in opposite direction to \(\hat{r}\).
03

Solve the integral

Executing the integral yields \(V = E_{0} \int_{R}^{0} (r / R)^{2} dr = [E_{0}(r^{3}/(3R^{2})]_{R}^{0} = \frac{1}{3} E_{0} R\).

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