Conceptual Questions:
1. A neutral conducting bar moves through a uniform magnetic field. The directions of B, v, and the length of the bar are all mutually perpendicular. Once equilibrium is reached, is an external force required to keep the bar moving with constant velocity? Explain.
2. Explain in words each of Maxwell's four equations (if this question is on the test, Max's eqns will be provided)
3. The operation of a tape player to play music depends on which of the following?
a. the Doppler effect
b. the photoelectric effect
c. the force acting on a current-carrying wire in a magnetic field
d. induced current from the motion of a magnet past a wire
4. According to Lenz's law the direction of an induced current in a conductor will be that which tends to produce which of the following effects?
a. It will enhance the effect which produces it.
b. It will produce a greater heating effect.
c. It will produce the greatest voltage.
d. It will oppose the effect which produces it.
5. If a bar magnet is falling through a loop of wire, the induced current in the loop of wire sets up a field which exerts a force on the magnet. This force between the magnet and the loop will be attractive when:
a. the magnet enters the loop.
b. the magnet is half way through.
c. the magnet is leaving the loop.
d. never.
6. Electricity may be generated by rotating a loop of wire between the poles of a magnet. The induced current is greatest when:
a. the plane of the loop is parallel to the magnetic field.
b. the plane of the loop is perpendicular to the magnetic field.
c. the magnetic flux through the loop is a maximum.
d. the plane of the loop makes an angle of 45 deg with the magnetic field.
7. A magnet moving past an object will produce eddy currents in the object if the object:
a. is magnetic material only.
b. is a conductor.
c. is an insulator.
d. is a liquid.
Numerical Problems: answers link to a help page.
1. A uniform 1.5 T magnetic field passes through the plane of a wire loop with area 0.3 m2. What flux passes through the loop when the direction of the 1.5 T field is at a 30 deg angle to the normal of the loop plane?
2. A 500 turn circular coil with an area of 0.05 m2 is mounted on a rotating frame which turns at a rate of 20 rad/s in the presence of a 0.05 T uniform magnetic field which is perpendicular to the axis of rotation. What is the instantaneous voltage in the coil at the moment that the normal to its plane is at a 90 deg angle to the field?
3. A large jetliner with a wing span of 40 m flies horizontally and due north at a speed of 300 m/s in a region where the magnetic field of the earth is 60 mT directed 50 deg below the horizontal. What is the magnitude of the induced voltage between the ends of the wing?
4. You can calculate the induced current in a ring by setting the voltage from a changing flux V = -DF/Dt equal to the voltage change -LDI/Dt in an inductor. If the magnetic field through a ring of area 1 cm2 collapses from 0.02 T to zero and the inductance of the ring is 10-7 H, what is the induced current in the ring?