Two small spherical balls of mass 10 g each with charges − 2 μ C and 2 μ C , are attached to two ends of very light rigid rod of length 20 cm. The arrangement is now placed near an infinite nonconduct

Question

Two small spherical balls of mass 10 g each with charges $- 2 μ C$ and $2 μ C$ , are attached to two ends of very light rigid rod of length 20 cm. The arrangement is now placed near an infinite nonconducting charge sheet with uniform charge density of $100 μ C / m^{2}$ such that length of rod makes an angle of $3 0^{\circ}$ with electric field generated by charge sheet. Net torque acting on the rod is:
(Take $ε_{0} : 8.85 \times 1 0^{- 12} C^{2} / Nm^{2}$ )

Question diagram: Two small spherical balls of mass 10 g each with charges − 2

Options:

Answer:

B

Solution:

$E τ = \frac{σ}{2 ε _{0}} = PE sin θ$
$= [(2 \times 1 0^{- 6}) (\frac{2}{10})] [\frac{100 \times 1 0 ^{- 6}}{2 \times 8.85 \times 1 0 ^{- 12}}] (\frac{1}{2}) = \frac{10}{8.85} = 1.12 Nm$

TestHub · Accepted Answer

E τ ​ = 2 ε 0 ​ σ ​ = PE sin θ ​ ​ = [ ( 2 × 1 0 − 6 ) ( 10 2 ​ ) ] [ 2 × 8.85 × 1 0 − 12 100 × 1 0 − 6 ​ ] ( 2 1 ​ ) = 8.85 10 ​ = 1.12 Nm ​

Physics - Elecrostatics Question with Solution | TestHub

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