Two point charges and are located at fixed positions in space

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

Problem

Two point charges

q_{1}

and

q_{2}

are located at fixed positions in space. (i) Define the displacement vector

\mathbf r_{12}

for the ordered pair

(q_{1},q_{2})

when the position vectors of the charges are

\mathbf r_{1}

and

\mathbf r_{2}

, respectively. (ii) Show how the corresponding unit vector

\hat{\mathbf r}_{12}

is obtained from

\mathbf r_{12}

and state its physical significance in expressing the electrostatic force. (iii) A charge

+4\,\mu\text{C}

is kept at

\bigl(3\,\text{cm},\,0,\,0\bigr)

and a charge

-4\,\mu\text{C}

is kept at

\bigl(-3\,\text{cm},\,0,\,0\bigr)

on the

x

-axis. Explain, without doing any numerical calculation, whether the electrostatic force on the right-hand charge is directed towards the left or towards the right, and justify your answer using the concepts introduced in parts (i) and (ii).

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