# NCERT Physics Class 12 Exemplar Ch 4 Moving Charges and Magnetism Part 3

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## Very Short Answer Types Questions

Q.12 Verify that the cyclotron frequency has the correct dimensions of .

Solution:

For a charge particle moving perpendicular to the magnetic field:

Q.13 Show that a force that does no work must be a velocity dependent force.

Solution:

must be velocity dependent which implies that angle between and is . If changes (direction) then (directions) should also change so that above condition is satisfied.

Q. 14 The magnetic force depends on **v** which depends on the inertial frame of reference. Does then the magnetic force differ from inertial frame to frame? Is it reasonable that the net acceleration has a different value in different frames of reference?

Solution:

Magnetic force is frame dependent. Net acceleration arising from this is however frame independent (non - relativistic physics) for inertial frames.

Q.15 Describe the motion of a charged particle in a cyclotron if the frequency of the radio frequency field were doubled.

Solution:

Particle will accelerate and decelerate alternatively. So the radius of path in the Dee’s will remain unchanged.

Q.16 Two long wires carrying current and are arranged as shown in Fig. The one carrying current is along is the axis. The other carrying current is along a line parallel to the axis given by and. Find the force exerted at because of the wire along the axis.

Solution:

At, the magnetic field due to is along the axis. The second wire is along theaxis and hence the force is zero.