(a) Derive the expression for the torque on a rectangular current carrying loop suspended in a uniform magnetic field.
(b) A proton and a deuteron having equal momenta enter in a region of uniform magnetic field at right angle to the direction of the field. Depict their trajectories in the field.

Explanation

(b) When a charged particle of charge .q. and momentum .p. enters in a region of uniform magnetic field `vecB` at right angle to the direction of the field, it describe a circular trajectory of radius
`r = p/(qB)`
As proton and deuteron have same charge and equal momenta, hence both will revolve in exactly the same circular path as shown fig.