$7.-5$ points An electron moving in the direction of the $\backslash (+$x $\backslash )-$axis enters a magnetic field. If the electron experiences a magnetic deflection in the $\backslash (-$y $\backslash )$ direction, the direction of the magnetic field in this region points in the direction of the

A$)\backslash (+$z $\backslash )-$axis.

B$)\backslash (-$z $\backslash )-$axis.

C$)\backslash (-$x $\backslash )-$axis.

D$)\backslash (+$y $\backslash )-$axis

E$)\backslash (-$y $\backslash )-$axis.

$8.-5$ points The figure shows a velocity selector that can be used to measure the speed of a charged particle. A beam of particles is directed along the axis of the instrument. A parallel plate capacitor sets up an electric field $\backslash ($ E $\backslash ),$ which is oriented perpendicular to a uniform magnetic field $\backslash ($ B $\backslash ).$ If the plates are separated by $2\mathrm{.}0$ mm and the value of the magnetic field is $0\mathrm{.}60$ T $,$ what voltage between the plates will allow particles of speed $5\mathrm{.}0\backslash (\backslash$times $105\backslash$mathrm$\{$~m$\}/\backslash$mathrm$\{$s$\}\backslash )$ to pass straight through without deflection? Show your work.

A

B$)1900$ V

C$)3800$ V

D$)190$ V

E$)94$ V

Answer:

$9.-5$ points A rigid rectangular loop, which measures $0\mathrm{.}30$ m by $0\mathrm{.}40$ m $,$ carries a current of $5\mathrm{.}5$ A $,$ as shown in the figure. A uniform external magnetic field of magnitude $2\mathrm{.}9$ T in the negative $\backslash ($ x $\backslash )$ direction is present. Segment $\backslash ($ C D $\backslash )$ is in the $\backslash ($ x z $\backslash )-$plane and forms a $\backslash (35^\{\backslash$circ$\}\backslash )$ angle with the $\backslash ($ z $\backslash )-$axis, as shown. Find the magnitude of the external torque needed to keep the loop in static equilibrium. Show your work.

$10.-\backslash (\backslash$mathbf$\{5\}\backslash )$ points A long straight conductor has a constant current flowing to the right. A wire rectangle is situated above the wire, and also has a constant current flowing through it $($as shown in the figure$).$ Which of the following statements is true?

A$)$ The net magnetic force on the wire rectangle is upward, and there is also a net torque on the it$.$

B$)$ The net magnetic force on the wire rectangle is zero, and the net torque on it is zero

C$)$ The net magnetic force on the wire rectangle is downward, and there is also a net torque on the it$.$

D$)$ The net magnetic force on the wire rectangle is zero, but there is a net torque on it$.$ E$)$ The net magnetic force on the wire rectangle is downward, and the net torque on it is zero.