Practice Test 7 - AP Physics 2

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

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1. A closed single-loop circuit contains an ideal battery and two resistors in series, $2.0\ \Omega$ and $4.0\ \Omega$. Which statement best describes the current in the $2.0\ \Omega$ resistor compared to the $4.0\ \Omega$ resistor?
2. A sealed container of fixed volume holds an ideal gas at $P_1=90\,\text{kPa}$ and $T_1=270\,\text{K}$. Some gas leaks out until $n_2=\tfrac{1}{2}n_1$ while temperature and volume remain constant. Compared to $P_1$, what is $P_2$?
3. A neutral metal can is charged by induction using a positively charged rod and a ground wire. After removing ground then rod, which statement best describes the can?
4. Two coherent water waves of the same frequency overlap at a point. The phase difference at that point is $\pi$ radians and the amplitudes are equal. Which result occurs at that point at that instant?
5. A single loop has an ideal battery $\mathcal{E}=6.0\text{ V}$ and two resistors $R_1=2.0\,\Omega$ and $R_2=1.0\,\Omega$ in series. The loop current $I$ is counterclockwise. Traverse counterclockwise starting at the battery's negative terminal. Sign convention: battery $(-\to +)$ is $+\mathcal{E}$; resistor in direction of current is $-IR$. Which equation correctly represents Kirchhoff's loop rule for the loop?
6. A fixed amount of gas in a piston-cylinder is the system. Use $\Delta U=Q-W$, with $Q>0$ into the system and $W>0$ done by the system. During a process, $Q=+90\ \text{J}$ and $\Delta U=-30\ \text{J}$. Which statement correctly describes the work $W$ done by the gas?
7. A toy is placed in front of a convex mirror on a lab cart. A student traces reflected rays and notes they diverge after reflection. Which statement best describes the image?
8. A pulse on a taut string reaches a rigid wall. The incident pulse travels to the right toward the wall, and the reflected pulse travels to the left away from the wall. Which statement correctly describes the reflection at the rigid boundary?
9. A student moves an object from far away toward a concave mirror until it is just inside the focal length. Which statement best describes the image at that final position? For object distances less than the focal length, reflected rays diverge and only appear to come from a point behind the mirror when extended backward. The image therefore cannot be projected on a screen in front of the mirror. Compared with the object, the apparent image is magnified due to the geometry of the diverging reflected rays.
10. A 2.0 cm tall arrow is placed in front of a concave mirror between the focal point $F$ and the center of curvature $C$. A ray diagram is drawn using a ray parallel to the principal axis and a ray through $F$. Which statement best describes the image?
11. A laser beam travels in water and strikes a water–air boundary at $25^\circ$ to the normal. Air has the lower refractive index ($n_{water} > n_{air}$). The beam transmits into the air. Compared to the incident ray, the refracted ray in air is at a(n) ____ angle to the normal.
12. A charged rod is brought near (not touching) a neutral metal sphere on an insulating stand, then removed. Which statement best describes the sphere's net charge?
13. A matte metal sphere is heated from 600 K to 900 K. Its emitted spectrum shifts so the peak wavelength decreases and the total intensity increases. As temperature increases, which statement correctly describes the spectrum?
14. An ideal $10\text{ V}$ battery connects to a parallel pair between junctions J and K: branch 1 has $R_1=5\,\Omega$, branch 2 has $R_2=10\,\Omega$. After junction K, the circuit continues through $R_3=5\,\Omega$ in series back to the battery. Which statement correctly compares the currents through $R_1$ and $R_2$?
15. In a vacuum tube, monochromatic light shines on a clean sodium surface. At $f=4.8\times10^{14}\,\text{Hz}$, electrons are emitted immediately; increasing intensity increases the current but the maximum electron kinetic energy is unchanged. At $f=3.9\times10^{14}\,\text{Hz}$, no electrons are emitted even after 60 s at very high intensity. Which statement best explains these observations?
16. A $6.0\,\Omega$ resistor and a $12\,\Omega$ resistor are connected in parallel to a $12\,\text{V}$ battery for $10\,\text{s}$. Which element dissipates the most power?
17. Two small spheres are separated by distance $r$. Sphere 1 has charge $+q$ and sphere 2 has charge $-2q$. Compared to the force magnitude at separation $r$, what is the force magnitude if the separation becomes $2r$?
18. X-ray photons scatter from electrons in graphite. The incident wavelength is $0.050\ \text{nm}$; at $180^\circ$ backscatter the wavelength becomes $0.0549\ \text{nm}$. Which conclusion about light is supported by this wavelength change?
19. In a closed loop, an ideal $5.0\,\text{V}$ battery and an ideal $11\,\text{V}$ battery oppose each other and are in series with a resistor $R=8.0\,\Omega$. Conventional current $I$ is clockwise. Traverse clockwise: $-$ to $+$ across a battery is $+\mathcal{E}$, and across the resistor with $I$ is $-IR$. Which equation satisfies Kirchhoff's loop rule?
20. A fixed source charge $-6.0\,\mu\text{C}$ is located at $x=+0.20\,\text{m}$ on the $x$ axis. Point $P$ is at the origin. A tiny positive test charge is placed at $P$ to sample the field and does not alter the source. Which statement best describes the direction of the electric field at $P$ due to the source charge?

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