# Physics 1251 Quiz 8

316 views
Since we won't have quiz 8 back before the exam, can somebody go over this quiz.
asked Nov 3, 2014 in General
edited Nov 4, 2014

Both versions of Quiz 8 were the same so these solutions should work for either section:

MC 1) B and E
Eddy currents occur in conducting material when the magnetic flux is changing, in this case by the moving magnet. The magnetic force applied because of the eddy currents will resist the motion involved, causing an increase in travel time. No Eddy currents occur in the magnets themselves or in the PVC.

MC 2) E
Inductors initially will resist current heavily by inducing current in the opposite direction of the applied current. The induced current will diminish over time as seen in answer choice (E). This is the opposite of how capacitors behave (a capacitor would initially have maximum current which decreases over time).

MC 3) A
Calculating the inductance of a solenoid with given number of turns, length, and cross-sectional area:

$$L=\frac{\mu_0 N^2 A}{l}=6.28mH$$

MC 4) A
Induced currents try to oppose changes in magnetic flux.

MC 5) A
(Left side of loop is closer) Magnetic field is directed towards the right and decreasing over time (which causes the magnetic flux to decrease as well). The induced current should oppose this decrease flux by inducing a magnetic field to the right. This corresponds to the induced current flowing in the direction shown.

MC 6) B
Calculating the energy stored in an inductor:
$$U=\frac{1}{2}L I_i^2$$
answered Nov 5, 2014 by (2,140 points)
edited Nov 5, 2014 by jcf1559