MHT CET · Physics · Electrostatics
Two charge metallic spheres are joined by a very thin metal wire. If the radius of the larger sphere is four times that of the smaller sphere, the electric field near the larger sphere is
- A twice that near the smaller sphere
- B quarter of that near the smaller sphere
- C same as that near the smaller sphere
- D half of that near smaller sphere
Answer & Solution
Correct Answer
(B) quarter of that near the smaller sphere
Step-by-step Solution
Detailed explanation
Since the spheres are joined by a metal wire, their potentials will be same.
Let the radius of the smaller sphere be \(r_1\) and the radius of the larger sphere be \(r_2=4 r_1\) the \(\mathrm{v}=\frac{1}{4 \pi \varepsilon_0} \cdot \frac{\mathrm{q}_1}{\mathrm{r}_1}=\frac{1}{4 \pi \varepsilon_0} \cdot \frac{\mathrm{q}_2}{\mathrm{r}_2}\)
\(
\therefore \frac{\mathrm{q}_2}{\mathrm{q}_1}=\frac{\mathrm{r}_2}{\mathrm{r}_1}
\)
The electric field near the surface of spheres are given by
\(
\begin{aligned}
& \mathrm{E}_1=\frac{1}{4 \pi \varepsilon_0} \cdot \frac{\mathrm{q}_1}{\mathrm{r}_1^2} \text { and } \mathrm{E}_2=\frac{1}{4 \pi \varepsilon_0} \cdot \frac{\mathrm{q}_2}{\mathrm{r}_2^2} \\
& \therefore \frac{\mathrm{E}_2}{\mathrm{E}_1}=\frac{\mathrm{q}_2}{\mathrm{q}_1} \cdot \frac{\mathrm{r}_1^2}{\mathrm{r}_2^2}=\frac{\mathrm{r}_2}{\mathrm{r}_1} \cdot \frac{\mathrm{r}_1^2}{\mathrm{r}_2^2}=\frac{\mathrm{r}_1}{\mathrm{r}_2}=\frac{1}{4}
\end{aligned}
\)
Let the radius of the smaller sphere be \(r_1\) and the radius of the larger sphere be \(r_2=4 r_1\) the \(\mathrm{v}=\frac{1}{4 \pi \varepsilon_0} \cdot \frac{\mathrm{q}_1}{\mathrm{r}_1}=\frac{1}{4 \pi \varepsilon_0} \cdot \frac{\mathrm{q}_2}{\mathrm{r}_2}\)
\(
\therefore \frac{\mathrm{q}_2}{\mathrm{q}_1}=\frac{\mathrm{r}_2}{\mathrm{r}_1}
\)
The electric field near the surface of spheres are given by
\(
\begin{aligned}
& \mathrm{E}_1=\frac{1}{4 \pi \varepsilon_0} \cdot \frac{\mathrm{q}_1}{\mathrm{r}_1^2} \text { and } \mathrm{E}_2=\frac{1}{4 \pi \varepsilon_0} \cdot \frac{\mathrm{q}_2}{\mathrm{r}_2^2} \\
& \therefore \frac{\mathrm{E}_2}{\mathrm{E}_1}=\frac{\mathrm{q}_2}{\mathrm{q}_1} \cdot \frac{\mathrm{r}_1^2}{\mathrm{r}_2^2}=\frac{\mathrm{r}_2}{\mathrm{r}_1} \cdot \frac{\mathrm{r}_1^2}{\mathrm{r}_2^2}=\frac{\mathrm{r}_1}{\mathrm{r}_2}=\frac{1}{4}
\end{aligned}
\)
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