Using Tsin? = FE and Tcos? = mg you can obtain an expression for the electric fo

Question

Using Tsin? = FE and Tcos? = mg you can obtain an expression for the electric force FE in terms of m and ?. Write then the angle ? in terms of distances y and z. The result of this is what we shall call equation 1. Write this equation in the write-up, Activity 2 section b.

Equation 1: FE =

Use your formula! Let us assume that we have a pithball with mass 6 g at the end of a string 18-cm long. When a charged rod is brought near the pithball, at the same height as the pithball, the ball is deflected 18 mm in the horizontal direction. What is the magnitude of the electrostatic force acting on the ball, in N?

Explanation / Answer

given T*sin(angle) = FE ..............eqn 1 T*cos(angle) = mg .............. eqn 2 dividing eqn 1 by eqn 2 gives tan(angle) = FE/(mg) so FE = (tan(angle))*(m*g) b) it deflected 1.8 cms and length of string is 18 cms cos( (90-angle) ) = 1.8/18 = 0.1 angle = 84.304 degrees FE = tan(84.304) * 0.006 * 9.8 = 0.585096945 N and the force is acting towards its right i.e. east wards.

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