q 14 2001
well, basically the angle between the current I and the magnetic field B in diagram X is not changing even thought the thing is rotating...
but in diagram Y, the angle between the current I and the magnetic field is changing, as the thing rotates in a circle...
hence for P, the angle is constant... F=BIl sin theta = constant
hence for Q, the angle is variable.....F=BIl sin theta = variable
The answer is C.
q 8 2002
this is related to the dotpoint: 'describe the forces experienced by a current-carrying loop in a magnetic field and describe the net result of these forces'. It is simply an application of the motor effect.
since the plane of the coil, is in line, or parallel to the magnetic field, thus, forces will be exerted only on the two sides, on the side (if you know what i mean). The top and bottom sides do not experience a force, because the current through them has a direction parallel to magnetic field, whereas the side sides have current which is perpendicular to the magnetic field. Use right hand rule, to find direction of forces on these side sides. You should get opposing forces, which has a rotating effect, called torque. The answer is C, again.
