Practice Test 10 - AP Physics 2

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

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1. At a junction, 2 A and 5 A enter, and one branch leaves 3 A. Another branch has current x, defined as entering. Find x.
2. A $12\text{ V}$ ideal battery feeds resistor $R_1=4\,\Omega$ to junction J. From J the circuit splits into two branches: top branch has $R_2=6\,\Omega$ to junction K; bottom branch has $R_3=3\,\Omega$ to K. The branches rejoin at K and return to the battery. Which statement correctly compares currents in the two branches at junction J?
3. An object is placed in front of a convex mirror at any finite distance. A ray diagram shows the image behind the mirror where ray extensions intersect. Which statement best describes the image?
4. A ceramic plate behaves approximately as a blackbody. When heated from 300 K to 600 K, the peak of its emitted spectrum moves to shorter wavelength while the curve's area increases. As temperature increases, what happens to the peak wavelength?
5. A student holds a small object 30 cm in front of a convex mirror. In a ray diagram, reflected rays diverge and their extensions intersect behind the mirror. Which statement best describes the image?
6. A metal is illuminated with light of fixed frequency above threshold. At low intensity, a small photoelectric current is measured. When intensity is tripled (same frequency), the photoelectric current triples, but the stopping potential remains unchanged. Which statement best matches these results?
7. A light ray reflects from a smooth surface. The incident ray makes $20^\circ$ with the surface (not the normal) and the reflected ray leaves on the other side. What is the reflected angle measured from the normal?
8. A gas in a piston-cylinder (system = gas) undergoes a process. Sign convention: $Q>0$ into system, $W>0$ done by system. The gas releases $120\,\text{J}$ of heat and $80\,\text{J}$ of work is done on the gas. Which statement correctly describes $\Delta U$?
9. A bar magnet is oriented vertically with its north pole at the top and south pole at the bottom. Point $W$ is located just outside the magnet near the side, halfway between the poles. Which statement best describes the magnetic field direction at point $W$?
10. A $0.040\ \text{nm}$ X-ray scatters from an electron and is measured at $0.041\ \text{nm}$. Which statement best accounts for the observed wavelength increase?
11. A charge $+q$ is separated by distance $r$ from a charge $-q$. If the $-q$ charge is moved to distance $3r$, the force on $+q$ is
12. A student proposes a cyclic engine that absorbs $600\,\text{J}$ of heat from a single thermal reservoir and produces $600\,\text{J}$ of work each cycle, with no other heat transfer. The proposed operation would be spontaneous once running. Which conclusion is consistent with the second law?
13. A Bohr atom has allowed levels $n=1,2,3$ and forbidden energies between; an electron is excited to $n=3$. Which statement correctly describes photon emission?
14. Two charged objects have charges $+3q$ and $-q$ separated by distance $r$. If both charges are doubled and distance is unchanged, the force magnitude becomes
15. A metal plate is heated from 500 K to 1000 K. Its emitted spectrum shifts so the peak wavelength decreases and the total intensity increases. As temperature increases, which statement correctly describes the photons emitted?
16. An ideal gas is sealed in a rigid tank (constant volume) so the amount of gas stays constant. The pressure changes from $P_1=100\ \text{kPa}$ to $P_2=250\ \text{kPa}$. Which statement correctly describes the final temperature $T_2$ in terms of $T_1$?
17. A $0.50\,\text{kg}$ metal block at $400\,\text{K}$ is placed in thermal contact with a $2.0\,\text{kg}$ water bath at $300\,\text{K}$ inside an insulated container. The block cools and the water warms until they reach a common final temperature; the process is spontaneous. Which statement best explains why the process occurs in the direction observed?
18. A cylindrical conductor has resistivity $\rho=2.0\times10^{-7}\,\Omega\cdot\text{m}$ (a material property). Its length is $1.0\,\text{m}$ and area is $2.0\times10^{-6}\,\text{m}^2$. Which change decreases its resistance the most?
19. A straight wire carries current into the page through a uniform magnetic field directed upward. Which statement best describes the magnetic force on the wire?
20. A light ray goes from air into a transparent liquid at $30^\circ$ to the normal. The liquid has higher refractive index than air ($n_{liquid} > n_{air}$). The ray enters the liquid. Compared to the incident ray, the refracted ray bends which way?

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