Question

(9) The diagrams show five possible orientations of a magnetic dipole in a uniform magnetic field B. For which of these does the magnetic torque on the dipole have the greatest magnitude? (10) A circular loop of wire rotates abo ut a diameter in a magnetic field that is perpendicular to the axis of rotation. Looking in the direction of the field at the loop the induced current is: A. Always clockwise B. Always counterclockwise C. Clockwise in the lower half of the loop and counterclockwise in the upper half D. Counterclockwise in the lower half of the loop and clockwise in the upper half Sometimes clockwise and sometimes counterclockwise E. (11) An RL series circuit is connected to an AC generator. If E 20.0V (power source) and the maximum potential difference across the resistor is 16.0 V, then the maximum potential difference across the inductor is: A. 25.6 V B. 36 V C. 2V D. 4 V E. 12 V (12) Which of the following is NOT true for electromagnetic waves? A. they transport energy B. they transport momentum C. they consist of changing electric and magnetic fields D. they travel at different speeds in vacuum, depending on their frequency E. they can be reflected

Please explain and answer 10, 11, 12

Answer 1

10)

The induced current is always in the direction so as to oppose the change in flux through the loop.

Assume the area vector of the loop is facing us in the beginning.At this moment, the angle between area vector and Magnetic field is 180 degrees.

Magnetic flux at this instant is BA cos180 = -BA

and after a half rvolution , angle becomes 0

Hence magnetic flux now becomes BA cos0 = BA

after 1 complete revolution , Magnetic Flux will become -BA again

the magnetic flux will keep oscillating between -BA and BA

Hence current ( change in mag flux / time) will also be oscillating.

Sometimes clockwise and sometimes anticlockwise

11)

At the particular moment when potential drop across resistor is 16 V, the potential drop across inductor is 4V

total potential drop has to be 20V

12)

EM waves travel at different speed in different media due to change in their wavelength , not frequency. The frequency remains the same.

Hence option D is the answer ( Its a false statement)