Assume that a stationary electron is a point of charge. What is the energy density u of its electric field at radial distances (a) r ! 1.00 mm, (b) r ! 1.00 mm, (c) r ! 1.00 nm, and (d) r ! 1.00 pm

See explanation.

Explanation:

The energy density of an electric field is given by

The electric field at a distance due to the electron is

therefore,

putting in values for and we get:

(a).

For

(b)

For

(c).

For

(d).

For

e

explanation:

there is no change in the electric potential energy as it is in rest on both conditions.

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