Practice Test 6 - AP Physics C Electricity and Magnetism

20 questions. Answer them in any order, then submit to see your score and every explanation.

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1. At time $t=0$, the switch is moved to position B. What is the current through resistor $R_2$ immediately after the switch is moved?
2. A $+1.0\,\mu\text{C}$ charge is placed at center of an insulating spherical shell; considering Gauss's Law, what is flux through the shell?
3. The magnetic permeability of a material, $\mu$, relates the magnetic field strength inside the material to the external magnetic field. For a paramagnetic substance, the value of $\mu$ is:
4. A $50 \, \Omega$ resistor is connected to a power source, resulting in a constant current of $0.50 \, \text{A}$. How much total thermal energy is dissipated in the resistor during a $2.0$-minute interval?
5. A uniform electric field $\vec{E}$ is directed along the +x-axis. A flat rectangular sheet of area $A$ lies in the x-y plane. What is the electric flux through this sheet?
6. A current $I$ flows radially outward from the center of a large conducting disk. Using Ampère's law with a circular Amperian loop centered on the disk, what can be concluded about the magnetic field?
7. Two identical solid conducting spheres, A and B, are isolated from their surroundings. Sphere A has a net charge of +Q and sphere B is electrically neutral. The spheres are brought into contact and then separated. What is the final net charge on sphere B?
8. Based on the description, a metal rod of length $L$ moves upward at speed $v$ through a uniform magnetic field $\vec{B}$ to the right, with the rod perpendicular to both $\vec{v}$ and $\vec{B}$. Charges in the rod experience the magnetic force $q\,\vec{v}\times\vec{B}$, separating charges and creating a motional EMF. For this geometry, $\mathcal{E}=BLv$, and if the rod is part of a closed circuit, a current flows. Lenz's Law predicts a magnetic force on the rod opposing its motion. How does Lenz's Law apply to the situation described?
9. Which of the following correctly compares the power $P_1$, $P_2$, and $P_3$ dissipated by the respective resistors?
10. A material is classified as non-ohmic. What does this classification imply about the material's resistance?
11. A positively charged rod is brought near, but does not touch, a neutral, isolated conducting sphere. The sphere is then connected to the ground with a conducting wire. What is the net charge on the sphere after the grounding wire is disconnected, and then the rod is removed?
12. A network of resistors with a total equivalent resistance $R_{ext}$ is connected to a battery with EMF $E$ and internal resistance $r$. The current flowing is $I$. If the same resistor network were connected to an ideal battery with the same EMF $E$, the current would be $I_{ideal}$. Which expression correctly relates $I_{ideal}$ to $I$?
13. Three point charges lie in the $xy$-plane: $q_1=+2.0\times10^{-9}\ \text{C}$, $q_2=-2.0\times10^{-9}\ \text{C}$, and $q_3=+1.0\times10^{-9}\ \text{C}$. A point $P$ is $0.30\ \text{m}$ from $q_1$, $0.30\ \text{m}$ from $q_2$, and $0.20\ \text{m}$ from $q_3$. Use superposition with $V=\sum kq_i/r_i$ (and $k=8.99\times10^{9}$, $e=1.60\times10^{-19}\ \text{C}$). In the situation described, what is the electric potential at point $P$ due to the charge configuration?
14. A proton is released from rest in a region of space with a non-uniform electric field. As the proton moves from point A to point B, its kinetic energy increases by $5.0 \times 10^{-16} \text{ J}$. What is the change in the electric potential energy of the proton-field system?
15. A $0.30\ \text{m}$ rod moves right at $6.0\ \text{m/s}$ through $B=0.80\ \text{T}$ into page; induced current direction?
16. A parallel-plate capacitor is charged by a battery to store energy $U_0$. The capacitor is then disconnected from the battery. The distance between the plates is then doubled. What is the new energy $U_f$ stored in the capacitor?
17. In the context of the electric field, calculate the change in electric potential energy for a $-2.0\,\mu\text{C}$ charge moving from 5 V to 25 V.
18. A square coil with $N$ turns and side length $s$ is in a uniform magnetic field $B$. The axis of the coil (normal to its plane) is initially parallel to the field. The coil is rotated by $90^\circ$ so its axis is perpendicular to the field. What is the magnitude of the magnetic flux through the entire coil in this final position?
19. After the spheres are separated, the charge remaining on the small sphere is $q$. Which statement is the best description of $q$?
20. For a series RC circuit connected to a DC voltage source at $t=0$, which of the following best describes the graph of the potential difference across the resistor, $V_R$, versus time?

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