Q.

Two small spherical balls of mass 10 g each with charges 2μC and 2μC, are attached to two ends of very light rigid rod of length 20 cm. The arrangement is now placed near an infinite non-conducting charge sheet with uniform charge density of 100 μC/m2 such that length of rod makes an angle of 30° with electric field generated by charge sheet. Net torque acting on the rod is: (Take ε0 : 8.85×1012 C2/Nm2)          [2025]

1 112 Nm  
2 1.12 Nm  
3 2.24 Nm  
4 11.2 Nm  

Ans.

(2)

E=σ2ε0=100×1062×8.85×1012N/C

τ=PE sin θ=qdE sin θ

      =2×106×0.2×100×1062×8.85×1012×12

 τ=1.12 Nm