Practice Test 8 - AP Physics C Electricity and Magnetism

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

Start practice test

1. Two point charges, $+2Q$ and $-Q$, are separated by a distance $d$. What is the change in electric potential energy of the system if the separation distance is decreased to $d/2$?
2. A conducting sphere of radius $R$ has a charge of $+2Q$. An identical, uncharged conducting sphere is brought into contact with it. After the spheres are separated, what is the charge on the first sphere?
3. Calculate the current at junction A: $I_T$ enters, then splits into $I_1=0.90\,\text{A}$ and $I_2=0.65\,\text{A}$ leaving along two branches.
4. When calculating the total electric flux through a closed three-dimensional surface, what is the standard convention for the direction of the differential area vector $d\vec{A}$?
5. Two coaxial solenoids with the same length $L$ have $N_1$ and $N_2$ turns respectively, carrying currents $I_1$ and $I_2$ in the same direction. What is the magnetic field inside both solenoids?
6. If $10^{20}$ electrons pass a given point in a wire every 2.0 seconds, what is the magnitude of the current in the wire?
7. A conducting spherical shell has net charge $Q=-2.0\,\text{nC}$. A spherical Gaussian surface of radius $r=0.30\,\text{m}$ is centered on it in air, and symmetry allows Gauss's Law. Considering the described process, if the charge is $-2.0\,\text{nC}$, what is the resulting electric field magnitude at $0.30\,\text{m}$?
8. An isolated, charged conducting object has a shape with one end being sharply pointed and the other end being rounded. When in electrostatic equilibrium, how does the surface charge density $\sigma$ at the pointed end compare to the surface charge density at the rounded end?
9. A student correctly states that the electric field inside a charged conductor in electrostatic equilibrium is zero. The student then claims that because the electric flux through any closed surface inside the conductor is zero, Gauss's law implies there can be no net charge enclosed by such a surface. Evaluate the student's reasoning.
10. An electric field is given by $\vec{E} = c z \hat{k}$, where $c$ is a positive constant. What is the electric flux through a circular disk of radius $R$ in the xy-plane, centered at the origin?
11. Two identical parallel-plate capacitors are connected in series. One capacitor contains air (κ = 1) and the other contains a dielectric with κ = 3. What is the equivalent capacitance of this combination?
12. A capacitor with capacitance $C$ is connected in series with a resistor $R$ and a battery with emf $E$. The circuit is allowed to reach a steady state, and the energy stored is $U$. If the capacitance is then changed to $2C$ while the battery and resistor remain the same, what is the new energy stored in the capacitor after a new steady state is reached?
13. A shielding demo uses a uniformly charged solid insulating sphere with radius $R=0.30\,\text{m}$ and volume charge density $\rho=+1.5\,\mu\text{C/m}^3$; a probe at $r=0.10\,\text{m}$ checks the predicted interior field. Consider the setup described above. Using Gauss's Law, determine the electric field inside the charged sphere.
14. In series $R=7\,\Omega$, $L=0.7\,\text{H}$, switch opens causing rapid current drop; Refer to the scenario above. Explain the significance of Lenz's Law in the scenario provided.
15. A point charge $Q=+3.0\ \mu\text{C}$ is fixed in vacuum. Based on the scenario described, calculate the electric field magnitude at $r=0.40\ \text{m}$ using Gauss's Law ($k=8.99\times10^{9}$).
16. In the context of the electric field, calculate the change in electric potential energy for a $-1.0\,\mu\text{C}$ charge moving 0.40 m along a uniform $300\,\text{V/m}$ field.
17. An ideal, constant voltage source $V$ is connected to a variable resistor of resistance $R$. How does the power $P$ dissipated by the resistor depend on its resistance $R$?
18. What is the effect of adding resistor $R_3$ on the total power dissipated by the circuit?
19. A current $I$ flows in a helical coil (like a spring) with $n$ turns per unit length. If the coil has a large length compared to its radius, what is the magnetic field inside the coil?
20. An isolated, neutral, solid conductor is suddenly placed in an external electric field. What is the primary cause for the redistribution of free charges that leads to electrostatic equilibrium?

Practice tests