A small sphere with mass m carries a positive charge q and is attached to one end of a silk fiber of length L. The other end of the fiber is attached to a large vertical insulating sheet that has a positive surface charge density s. Show that when the sphere

is in equilibrium, the fiber makes an angle equal to arctan(σq2εomg)with the vertical sheet.

Short Answer

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Proven below

Step by step solution

01

Step 1:

Required: Proven thatθ=arctanσq2εomg

02

Figure

03

Calculation

The electric field of the infinite sheet is given by

E=σ2εo (1)

So the force acting on the ball is given by

F=E=σq2εo (2)

The electric force is equal to the tension component

Tsin(θ)=σq2εo (3)

And the vertical component is equal to the weight

Tsin(θ)=mg (4)

Dividing (3) on (4) to get

tan(θ)=σq2mgεoθ=arctanσq2εomg

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