Practice Test 8 - 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 string fixed at both ends shows a standing wave with nodes at $x=0$ and $x=L$ and antinodes at $x=\frac{L}{4}$ and $x=\frac{3L}{4}$. This pattern remains stationary while the string oscillates. Which statement about the nodes is correct?
2. In a Bohr-model atom, allowed energies are $E_1, E_2, E_3$ with forbidden energies between them. Which event must produce a photon with energy $E_3-E_1$?
3. A 3.0 cm-tall object is placed in front of a concave mirror farther than $C$. A ray diagram shows the image forming between $F$ and $C$. Which statement best describes the image?
4. Two trials use the same metal. Trial 1: light at frequency just above threshold produces electrons with low maximum kinetic energy. Trial 2: frequency is unchanged but intensity is tripled, producing three times as many electrons per second with the same maximum kinetic energy. Which statement best accounts for this result?
5. In the Bohr model, electrons occupy discrete allowed energies $E_1<E_2<E_3<E_4$ (forbidden: energies between). Which statement best describes emission during a transition?
6. A loop contains an ideal $15\text{ V}$ battery in series with three resistors: $R_1=1\,\Omega$, $R_2=2\,\Omega$, and $R_3=3\,\Omega$. The current $I$ is clockwise. Traverse clockwise: battery from $-$ to $+$ is $+15$, and each resistor with the current is a drop $-IR$. Which equation correctly represents the loop?
7. A pulse on a rope transfers energy; a student doubles the pulse amplitude without changing the medium. Which statement best describes the wave speed?
8. A singly charged ion ($q=+e$) moves due north at $v=1.2\times10^{6}\,\text{m/s}$ through a region where $B=0.50\,\text{T}$ points upward. No electric field is present. Which statement best describes the direction of the magnetic force on the ion?
9. Inside a star, two $^{2}\mathrm{H}$ nuclei combine to form $^{4}\mathrm{He}$ and release energy. Which process occurs in the star's core?
10. In a cool gas, an electron absorbs a photon and moves to a higher energy level. The absorbed photon's energy must equal
11. A $2.0\,\mu\text{F}$ capacitor is connected to a $10\,\text{V}$ ideal battery. Which statement best describes the voltage across the capacitor?
12. In the Sun, net fusion converts four protons into one $^{4}\text{He}$ nucleus plus other particles. Which statement best explains why energy is released?
13. A capacitor is discharging through a resistor after being fully charged. Which statement best describes the resistor's power dissipation as time increases?
14. Two metal blocks, R and S, start at $30^\circ\text{C}$ and are cooled by removing the same thermal energy, $Q=3.0\,\text{kJ}$, from each. Their masses are equal, but $c_R=500\,\text{J/(kg\,K)}$ and $c_S=1000\,\text{J/(kg\,K)}$. (Specific heat determines $|\Delta T|$ for fixed $Q$; conductivity affects cooling rate.) Which block's temperature decreases least?
15. A cup of hot coffee cools from $70^\circ\text{C}$ to room temperature $22^\circ\text{C}$ in still air (spontaneous). Which statement best describes the entropy change of the coffee itself?
16. Two slits are illuminated by the same laser so the waves leaving the slits have a constant phase relationship. On the screen, the central bright fringe occurs where the path difference is zero. Which change increases the spacing between adjacent bright fringes on the screen without requiring any calculation?​
17. Two circular loops share the same center and lie in the plane of the page. The inner loop has radius $2.0\ \text{cm}$ and carries $1.0\ \text{A}$ counterclockwise; the outer loop has radius $4.0\ \text{cm}$ and carries $1.0\ \text{A}$ counterclockwise. Which statement best describes the magnetic field magnitude at the common center?
18. A capacitor is discharging through a resistor. Which statement best describes the magnitude of the current as time increases?
19. A nucleus undergoes beta-minus decay. Which change to the nucleus's atomic number $Z$ occurs?
20. A student stands in front of a convex mirror used as a hallway safety mirror. The student is several meters from the mirror, much farther than the focal length. Which statement best describes the image?

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