Practice Test 1 - 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. A conducting rod moves right at $4.0\ \text{m/s}$ through $B=0.60\ \text{T}$ out of page; induced current direction?
2. What is the physical significance of the time constant, $\tau = L/R$, for this circuit?
3. A parallel-plate capacitor has uniform field between plates and plate separation $d=2.0\times10^{-3}\ \text{m}$. The field magnitude is $E=5.0\times10^{4}\ \text{V/m}$ directed from the positive plate to the negative plate. Use $\Delta V=Ed$ (magnitude) and $k=8.99\times10^{9}$, $e=1.60\times10^{-19}\ \text{C}$. In the situation described, calculate the potential difference between plates (positive minus negative).
4. An air-filled parallel-plate capacitor has a capacitance of $C_0$. If the area of the plates is tripled and the distance between the plates is halved, what is the new capacitance?
5. Which of the following best defines an electrical loop within a circuit?
6. An ideal LC circuit has a total electromagnetic energy of $50$ $\mu$J. At a certain instant, the energy stored in the electric field of the capacitor is $30$ $\mu$J. What is the energy stored in the magnetic field of the inductor at that same instant?
7. A reading lamp uses a bulb modeled as a $R=60\,\Omega$ resistor connected to a $12\,\text{V}$ supply in a simple lighting circuit. The voltage across the bulb remains $12\,\text{V}$ during operation. Use $P=\frac{V^2}{R}$ to compute the bulb's power usage. Report the result in watts (W). What is the power usage of the light bulb?
8. Wire A has length $L$ and radius $r$. Wire B, made from the same uniform material, has length $2L$ and radius $r/2$. What is the ratio of the resistance of Wire B to the resistance of Wire A, $R_B/R_A$?
9. A single resistor $R_1$ is connected to an ideal battery, dissipating a total power $P$. A second resistor $R_2$ is then connected in series with $R_1$. How does the new total power dissipated by the circuit compare to $P$?
10. A series $R=4\,\Omega$, $L=2\,\text{H}$ is connected to $8\,\text{V}$ at $t=0$; Refer to the scenario above. How does the current change over time after the switch is closed?
11. A cylindrical conductor has a non-uniform current density given by $J(r) = J_0 (1 - r/R)$, where $J_0$ is a constant, $R$ is the radius of the conductor, and $r$ is the radial distance from the center. What is the total current $I$ flowing through the conductor?
12. A component is fabricated from a material of uniform resistivity $\rho$. The component has a length $L$ and a circular cross-section. Its radius varies linearly with position $x$ along its length, from $r=a$ at $x=0$ to $r=b$ at $x=L$. What is the electrical resistance of this component?
13. A rectangular wire loop is pulled at a constant speed $v$ out of a region of uniform magnetic field $B$. This results in a magnetic braking force of magnitude $F_0$. If the experiment is repeated with a magnetic field of strength $2B$, but all other parameters (loop dimensions, resistance, speed) remain the same, what will be the new magnetic braking force?
14. What is the primary reason for this delay in the current reaching its maximum value?
15. Which of the following statements correctly describes the magnetic field lines produced by a permanent bar magnet?
16. Which of the following describes the current $I(t)$ in the resistor for $t > 0$?
17. A power supply has an emf of $24 \, \text{V}$ and an internal resistance of $2.0 \, \Omega$. To which of the following load resistances will the power supply deliver the most power?
18. A uniform electric field of magnitude $E=2.5\times10^{3}\,\text{N/C}$ points to the right. Two points lie on the field line, separated by $d=0.040\,\text{m}$, with $A$ to the left of $B$. Use $\Delta V=V_B-V_A=-Ed$ and $V=Ed$ for magnitude. In the situation described, calculate the potential difference between points $A$ and $B$.
19. For a closed surface, the net electric flux is measured to be negative. Which statement correctly describes the electric field and the net charge inside the surface?
20. What is the current flowing through the $3\,\Omega$ resistor?

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