Two point charges of magnitudes and are kept fixed in vacuum at a separation of along…

PHYSICS · Multi-part · A Level · Physics · Fields and their consequences · Fields and their consequences

Problem

Two point charges of magnitudes

+5\,\mu\text{C}

and

+20\,\mu\text{C}

are kept fixed in vacuum at a separation of

40\,\text{cm}

along a straight line. (i) Write an expression for the magnitude of the electrostatic force acting on a small positive test charge

q

placed at a point P located at a distance

x

from the

+5\,\mu\text{C}

charge along the line joining the two fixed charges. (ii) Calculate the value of

x

for which the net force on the test charge

q

becomes zero. Express your answer in centimetres measured from the

+5\,\mu\text{C}

charge. (iii) From your result, state whether the point P lies closer to the

+20\,\mu\text{C}

charge or to the

+5\,\mu\text{C}

charge, and briefly explain why.