Practice Test 4 - 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 gas in a piston-cylinder is the system. Take $Q>0$ into the gas and $W>0$ done by the gas. During a process the gas does $W=+300\,\text{J}$ of work, and its internal energy does not change ($\Delta U=0$). Which statement correctly describes the heat transfer?
2. A speaker produces a steady tone in air where the sound speed is $v$. If the frequency is increased, which statement correctly relates the wavelength change?
3. In a copper wire, a steady stream of $2.0\times10^{18}$ electrons passes a point each second from left to right. Which statement best describes the conventional current direction?
4. A straight horizontal wire carries $I=3.0\,\text{A}$ to the right through a uniform magnetic field $\vec B$ into the page. Which statement best describes the magnetic force on the wire segment in the field?
5. A student places a $25^\circ\text{C}$ glass beaker in direct contact with a $90^\circ\text{C}$ hot plate. The beaker is initially cooler than the hot plate, and they remain in contact until the beaker's temperature stops changing. Which statement best describes the thermal energy flow while they approach equilibrium?
6. A radar pulse travels through air toward an aircraft. At a point in space, the electric field points upward while the magnetic field points to the right, and the pulse moves forward. Which statement best describes electromagnetic waves?
7. An ideal $20\,\text{V}$ source drives $R_1=10\,\Omega$ in series with a parallel network between junctions $C$ and $D$. The top branch contains $R_2=10\,\Omega$ and the bottom branch contains $R_3=30\,\Omega$; the branches recombine at $D$. At junction $C$, which statement correctly compares the branch currents?
8. A $3\ \Omega$ resistor has a constant current of $2\ \text{A}$ for $4\ \text{s}$. The voltage across it is $V=IR$ and the power is $P=IV$. Which statement about its power is correct?
9. A solenoid is oriented horizontally with its axis along $+x$. The conventional current around the windings is counterclockwise when viewed from the left end. Which statement best describes the direction of the magnetic field inside the solenoid?
10. An ideal $5\text{ V}$ battery connects to $R_1=1\,\Omega$ in series, then reaches junction J. From J to junction K, two parallel branches contain $R_2=1\,\Omega$ and $R_3=2\,\Omega$. The branches rejoin at K and return. Which statement correctly compares the charge per second entering junction J to the total leaving J?
11. A steady current of $0.40\ \text{A}$ flows in a wire from north to south. Which statement best describes the motion of the electrons in the wire?
12. Two devices A and B each operate for the same time interval. Device A has constant $V$ and draws constant current $I$. Device B has the same $V$ but draws $2I$. Compared to A, B's power is
13. A monochromatic laser passes through a single narrow slit. The slit width is much larger than the wavelength $\lambda$, producing only slight spreading. Which change produces the greatest diffraction spreading on a distant screen?
14. An external agent performs $+10 \text{ J}$ of work to move a charge at a constant speed from point X to point Y in an electric field. What is the change in the electric potential energy of the charge-field system?
15. A plane mirror is mounted vertically. A laser beam in air strikes the mirror; the incident ray travels down and to the left at $20^\circ$ to the normal. The reflected ray leaves traveling down and to the right. The reflected ray makes which angle with the normal?
16. A loop contains two series batteries, $9.0\text{ V}$ and $3.0\text{ V}$, oriented so their emfs oppose. A resistor $R=6.0\,\Omega$ is also in series. Current $I$ is counterclockwise. Traverse counterclockwise: across a battery from $-$ to $+$ is $+\mathcal{E}$, from $+$ to $-$ is $-\mathcal{E}$; across the resistor in the direction of current is $-IR$. Which equation satisfies Kirchhoff's loop rule?
17. Two point charges $+q$ and $-q$ are separated by distance $r$. Compared to the force magnitude on either charge, what happens if both charges are tripled to $+3q$ and $-3q$ while $r$ stays the same?
18. An atom absorbs a photon and later emits a photon of the same energy, producing an absorption line in transmission. Which statement best explains the initial absorption step?
19. In a Compton scattering experiment, X-rays of known wavelength scatter from electrons, and the scattered wavelength increases with scattering angle. Classical wave scattering cannot explain a wavelength change that depends on angle and target electrons. Which statement best explains the shift?
20. A sealed, rigid container is divided by a removable partition. Side A contains an ideal gas; side B is vacuum. The partition is removed and the gas freely expands to fill the whole container; no heat enters and no work is done. The expansion is spontaneous. Which statement best explains why it occurs?

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