two small charges with a mass of 1 gram each are connected by 2 cm long insulati

Question

two small charges with a mass of 1 gram each are connected by 2 cm long insulating rod of negligible mass. Each ball has the same magnitude of charge 10 nC, but with opposite sign. The rod is held in a 1e4 N/C uniform electric field at the angle of 30 degrees, then released to rotate around its center of mass.

a. What is the dipole moment of the rod?

b. Calculate the magnitude of the torque exerted on the rod by the electric field.

c. Obtain the moment of inertia around the center of mass.

d. What is the initial angular acceleration when the rod is released?

Explanation / Answer

a) qd = 10*10^-9*0.02 = 2*10^-10 Cm

b) torque = p X E = 2*10^-10*1*10^4*sin30 = 1*10^-6 Nm

c) I = 2*0.004*0.02^2 = 3.2*10^-6 kgm^2

d) 10^-6/3.2*10^-6 = 1/3.2 = 0.3125 rad/s^2

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