k

A$)0\mathrm{.}79$ mA

B$)3\mathrm{.}9$ mA

C$)1\mathrm{.}7$ mA

D$)2\mathrm{.}1$ mA

E$)0\mathrm{.}20$ mA

$15.-5$ points A bar magnet is held vertically with its upper end a little bit below the center of a horizontal metal ring. The upper end of the magnet is its north pole, as shown in the figure. The bar magnet is now dropped. An observer views the ring from above its center. To this observer, how will the induced current in the ring behave as the magnet falls?

A$)$ The current will flow clockwise and be increasing.

B$)$ The current will flow clockwise and be decreasing.

C$)$ The current will flow counter$-$clockwise and be increasing.

D$)$ The current will flow counter$-$clockwise and be decreasing.

E$)$ The induced current will be zero.

$16.-5$ points In the figure, two parallel wires carry currents of magnitude $\backslash ($ I $\backslash )$ in opposite directions. A rectangular loop is midway between the wires. The current $\backslash ($ I $\backslash )$ is decreasing with time. The induced current through the resistor $\backslash ($ R $\backslash )$ is

A$)$ from $\backslash ($ a $\backslash )$ to $\backslash ($ b $\backslash ).$

B$)$ from $\backslash ($ b $\backslash )$ to $\backslash ($ a $\backslash ).$

C$)$ There is no induced current through the resistor.

$17.-5$ points $\backslash (\backslash$underline$\{\backslash$underline$\{$A s$\}\}\backslash )$ shown in the figure, a wire and a $\backslash (10-\backslash$Omega $\backslash )$ resistor are used to form a circuit in the shape of a square, $20$ cm by $20$ cm $.$ A uniform but nonsteady magnetic field is directed into the plane of the circuit. The magnitude of the magnetic field is decreased from $1\mathrm{.}50$ T to $0\mathrm{.}50$ T in a time interval of $63$ ms $.$ The average induced current and its direction through the resistor, in this time interval, are closest to

Show your work.

A$)63$ mA $,$ from $\backslash ($ b $\backslash )$ to $\backslash ($ a $\backslash ).$

B$)38$ mA $,$ from $\backslash ($ b $\backslash )$ to $\backslash ($ a $\backslash ).$

C$)63$ mA $,$ from $\backslash ($ a $\backslash )$ to $\backslash ($ b $\backslash ).$

D$)38$ mA $,$ from $\backslash ($ a $\backslash )$ to $\backslash ($ b $\backslash ).$

E$)95$ mA $,$ from $\backslash ($ a $\backslash )$ to $\backslash ($ b $\backslash ).$