Q.

Two charges each of magnitude 0.01 C and separated by a distance of 0.4 mm constitute an electric dipole. If the dipole is placed in an uniform electric field 'E' of 10 dyne/C making 30° angle with E, the magnitude of torque acting on the dipole is               [2023]

1 4.0×10-10 Nm  
2 2.0×10-10 Nm  
3 1.0×10-8 Nm  
4 1.5×10-9 Nm  

Ans.

(2)

|P|=qd=0.04×0.4×10-3=4×10-6

|τ|=PEsinθ=4×10-6×10×10-5×sin30°

        =4×10-6-5+1×12=2×10-10