Electricity and Magnetism
# Electric Fields

$3 \times 10^6\text{ V/m}$.

Lightning occurs when there is a breakdown in the electrical insulating properties of air. That is, the potential difference between the ground and a cloud is so great that it overcomes the fact that air usually a pretty good insulator. Air begins to conduct at a potential difference of approximatelyA typical height for a cloud to ground lightning strike is 1 km.

What is the total voltage difference between the cloud and the ground right before the lightning strike **in Volts**?

$ABC.$ Initially the charge of the sphere at point $A$ is $q_{A}=0$ and the spheres at $B$ and $C$ carry the same charge $q_{B}=q_{C}=q.$ It is known that the sphere $B$ exerts an electrostatic force on $C$ which has a magnitude $F=4~\mbox{N}.$ Suppose an engineer connects a very thin conducting wire between spheres $A$ and $B.$ Then she removes the wire and connects it between spheres $A$ and $C.$ After these operations, what is the magnitude of the force of interaction **in Newtons** between $B$ and $C?$

A thin disc of radius $\displaystyle R = 10 \text{ cm }$made of non-conducting material is charged uniformly so as to acquire a uniform surface charge density $\displaystyle \sigma = 5 \text{ nC}/\text{m}^2$.

Find the potential at the edge of the disc in **Volts**.

**Details and Assumptions**

- $\displaystyle \frac{1}{4 \pi \epsilon _{0} } = 9 \times 10^{9} \text{ N}\cdot \text{m}^2 / \text{C}^2$