Two point charges are fixed on a straight line: a charge at and a charge at
PHYSICS · Multi-part · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
Two point charges are fixed on a straight line: a charge +Q at x=0 and a charge −4Q at x=d. A unit positive test charge is brought anywhere along the same line.
Find the position(s) on the x–axis where this test charge would experience zero net electrostatic force.
(i) Set up the required algebraic equation in the coordinate x (measured from the charge +Q) for the condition of zero net force.
(ii) Solve the equation obtained to express the possible value(s) of x in terms of d.
(iii) State clearly whether the equilibrium position lies between the two fixed charges or outside the interval 0≤x≤d, giving reasons based on your solution.