Q.

An electric dipole is placed at an angle of 30° with an electric field intensity 2×105N C-1. It experiences a torque equal to 4 N m. The charge on the dipole, if the dipole length is 2 cm, is             [2016]
 

1 8 mC  
2 2 mC  
3 5 mC  
4 μC  

Ans.

(2)

Here, θ=30°,E=2×105N C-1,τ=4Nm

l=2 cm=0.02 m, q=? ; τ=pEsinθ=(ql)Esinθ

   q=τElsinθ=42×105×0.02×12

           =42×103=2×10-3C=2 mC