Question

An electric dipole consists of charges +2e and -2e separated by 0.76 nm. It is in an electric field of strength 4.8 × 106 N/C. Calculate the magnitude of the torque on the dipole when the dipole moment is (a) parallel to, (b) perpendicular to, and (c) antiparallel to the electric field.

Answer 1

given

q = 2*e

= 2*1.6*10^-19 C

d = 0.76 nm

= 0.76*10^-9 m

E = 4.8*10^6 N/C

dipole moment of the dipole, P = q*d

= 2*1.6*10^-19*0.76*10^-9

= 2.43*10^-28 C.m

we know, Torque acting on the dipole, T = P cross E

= P*E*sin(theta)

a) when E is parallel to p, theta = 0

T = P*E*sin(0)

= 0 N.m <<<<<<<---------------Answer

b) when E is perpendicular to p, theta = 0

T = P*E*sin(90)

= 2.43*10^-28*4.8*10^6*sin(90)

= 1.17*10^-21 N.m <<<<<<<---------------Answer

c) when E is anti parallel to p, theta = 180

T = P*E*sin(180)

= 0 N.m <<<<<<<---------------Answer