A Van de Graaff generator produces sparks when the field strength at its surface is $4.0 \times 10^{4} \mathrm{~V} \mathrm{~cm}^{-1}$. If the diameter of the sphere is $40 \mathrm{~cm}$, what is the charge on it?

(a) What is the electrical potential energy of a charge of $+1 \mathrm{C}$ placed at each of the points $\mathrm{A}$, $\mathrm{B}, \mathrm{C}, \mathrm{D}$ between the charged, parallel plates shown in Figure $22.15 ?$

(b) What would be the potential energy of $\mathrm{a}+2 \mathrm{C}$ charge at each of these points? (C is halfway between $\mathrm{A}$ and $\mathrm{B}, \mathrm{D}$ is halfway between $\mathrm{C}$ and B.)

A Van de Graaff generator has a spherical dome of radius $10 \mathrm{~cm}$. It is charged up to a potential of $100000 \mathrm{~V}(100 \mathrm{kV}) .$ How much charge is stored on the dome? What is the potential at a distance of $20 \mathrm{~cm}$ from the dome?

How much work is done in moving $\mathrm{a}+1 \mathrm{C}$ charge along the following paths shown in Figure 22.16: from $\mathrm{E}$ to $\mathrm{H}$; from $\mathrm{E}$ to $\mathrm{F}$; from $\mathrm{F}$ to $\mathrm{G} ;$ from $\mathrm{H}$ to $\mathrm{E}$ ?

A uniform electric field.

How much work is done in moving $\mathrm{a}-1 \mathrm{C}$ charge along the following paths shown in Figure 22.16: from $\mathrm{E}$ to $\mathrm{H}$; from $\mathrm{E}$ to $\mathrm{F}$; from $\mathrm{F}$ to $\mathrm{G} ;$ from $\mathrm{H}$ to $\mathrm{E}$ ?

A uniform electric field.

How much work is done in moving $\mathrm{a}+2 \mathrm{C}$ charge along the following paths shown in Figure 22.16: from $\mathrm{E}$ to $\mathrm{H}$; from $\mathrm{E}$ to $\mathrm{F}$; from $\mathrm{F}$ to $\mathrm{G} ;$ from $\mathrm{H}$ to $\mathrm{E}$ ?

A uniform electric field.

We showed that in the atomic nuclei the electric force is much larger than the gravitational force . Is this also true in the formation of atoms? Yet, in the formation of stars and planetary systems, the gravitational force rules.

Discus and explain why there is this difference.