A pendulum bob of mass 80mg and carrying a charge of `2xx 10^(-8)C` is at rest in a uniform, horizontal electric field of 20 `kVm^-1.` Find the tension in the thread.

Explanation

from the figure,
` Tcos theta=mg…..(i) `
` Tsin theta=qE…..(ii) `
` tan theta=(qE)/(mg )`
` =(20xx10^3xx2xx10^-8 )/(80xx10^-6xx9.8 )`
` tan theta=40/(8xx9.8) `
` =0.51 `
` theta=27^@ `
From equation (i),
` T=(mg)/(cos theta)=(80xx10^-6xx9.8) /cos27^@ `
` T=8.8xx10^-4N`.