Question

At which point on this electric field will a test charge show the maximum strength?
A
B
C
D

Answer 1

Answer:

A

Explanation:

The figure shows the electric field produced by a spherical charge distribution - this is a radial field, whose strength decreases as the inverse of the square of the distance from the centre of the charge:

$E\propto \frac{1}{r^2}$

More precisely, the strength of the field at a distance r from the centre of the sphere is

$E=k\frac{Q}{r^2}$

where k is the Coulomb's constant and Q is the charge on the sphere.

From the equation, we see that the field strength decreases as we move away from the sphere: therefore, the strength is maximum for the point closest to the sphere, which is point A.

This can also be seen from the density of field lines: in fact, the closer the field lines, the stronger the field. Point A is the point where the lines have highest density, therefore it is also the point where the field is strongest.