Read the text carefully and answer the questions:
When electric dipole is placed in uniform electric field, its two charges experience equal and opposite forces, which cancel each other and hence net force on electric dipole in uniform electric field is zero. However these forces are not collinear, so they give rise to some torque on the dipole. Since net force on electric dipole in uniform electric field is zero. so no work is done in moving the electric dipole in uniform electric field. However some work is done in rotating the dipole against the torque acting on it.
a. The dipole moment of a dipole in a uniform external field E is P. Then the torque τ acting on the dipole is:
a) τ=2(P+E)
b) τ=P⋅E
c) τ=(P+E)
d) τ=P×E
b. An electric dipole consists of two opposite charges, each of magnitude 1.0μC separated by a distance of 2.0cm. The dipole is placed in an external field of 105 NC−1. The maximum torque on the dipole is:
a) 4×10−3 Nm
b) 2×10−3 Nm
c) 1×10−3 Nm
d) 0.2×10−3 Nm
c. Torque on a dipole in a uniform electric field is minimum when θ is equal to:
a) 0∘
b) 90∘
c) 180∘
d) Both 0∘ and 180∘
d. When an electric dipole is held at an angle in a uniform electric field, the net force F and torque τ on the dipole are:
a) F=0,τ=0
b) F=0,τ=0
c) F=0,τ=0
d) F=0,τ=0