Two point charges and are fixed at points and respectively on a straight line

PHYSICS · Subjective · A Level · Physics · Fields and their consequences · Fields and their consequences

Problem

Two point charges

Q_1

and

Q_2

are fixed at points

x=0

and

x=d

respectively on a straight line. (i) Derive an expression for the position

x

(measured from

Q_1

) where the net electric field on the line becomes zero. Express your result in terms of

Q_1,\;Q_2

and

d

. (ii) On the basis of the derived expression, state the condition under which the null point lies (a) between the two charges, (b) to the left of

Q_1

, and (c) to the right of

Q_2

. (iii) For

Q_1=+4.0\,\mu\text{C}

Q_2=-9.0\,\mu\text{C}

and

d=0.50\,\text{m}

, obtain the exact position(s) of the null point(s) and verify by calculation that the net field indeed vanishes at that point.