# HELP ME WITH ELECTRO PHYSICS!!!!!?

Two charges are placed on the x-axis, an unknown positive charge at x=0 cm and a negative 2.335 mC charge at 2.171 cm from the origin. Calculate the magnitude of the charge at x=0 cm which causes the total electric field at 11.267 cm to be zero.

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• 9 years ago

It's easy.

Let's calculate the intensity of the electric field E1 which produces negative charge at x = 11.267 cm.

E1 = k*Q1/R1^2, where R1 = (11.267-2.171)*10^-2 = 9.096 * 10^-2 m

The same intensity of the electric field E2 must produce positive charge. E2 = E1. They are in opposite directions.

E2 = k *Q2/R2^2 , where R2 = 11.267 cm.

k*Q1/R1^2 = k *Q2/R2^2

Q2 = Q1 * R2^2/R1^2 = 2.335 * 10^-3 * 11.267^2 /9.096^2 = 3.583 * 10^-3 = +3.583 mC

Good luck!