MCAT Physics Flashcards

24 sample cards from the Physics deck

Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.

1. State Coulomb's law for the force between two point charges.

   $F = k\frac{|q_{1}q_{2}|}{r^{2}}$, where $k \approx 8.99\times10^{9}\ \text{N·m}^{2}/\text{C}^{2}$. The force is attractive for opposite charges and repulsive for like charges.

2. Define the electric field and give the field of a point charge.

   Electric field is force per unit positive test charge: $\vec{E} = \frac{\vec{F}}{q}$. For a point charge: $E = k\frac{|Q|}{r^{2}}$, pointing away from positive and toward negative charge.

3. Relate electric potential energy and electric potential for point charges.

   Potential energy: $U = k\frac{q_{1}q_{2}}{r}$. Electric potential (per unit charge): $V = k\frac{Q}{r}$, so $U = qV$. Potential is a scalar.

4. State Ohm's law and the formula for electrical power dissipated.

   Ohm's law: $V = IR$. Power dissipated: $P = IV = I^{2}R = \frac{V^{2}}{R}$.

5. How do resistors combine in series versus parallel?

   Series: $R_{eq} = R_{1} + R_{2} + \cdots$. Parallel: $\frac{1}{R_{eq}} = \frac{1}{R_{1}} + \frac{1}{R_{2}} + \cdots$, so the parallel equivalent is always smaller than the smallest resistor.

6. How do capacitors combine in series versus parallel, and what is stored energy?

   Series: $\frac{1}{C_{eq}} = \sum \frac{1}{C_{i}}$. Parallel: $C_{eq} = \sum C_{i}$. Energy stored: $U = \frac{1}{2}CV^{2} = \frac{Q^{2}}{2C}$. Capacitance: $C = \frac{Q}{V}$.

7. State Kirchhoff's two circuit laws.

   Junction (current) rule: $\sum I_{in} = \sum I_{out}$ (charge conservation). Loop (voltage) rule: the sum of potential changes around any closed loop is zero, $\sum \Delta V = 0$ (energy conservation).

8. Give the magnetic force on a moving charge and on a current-carrying wire.

   On a charge: $\vec{F} = q\vec{v}\times\vec{B}$, magnitude $F = qvB\sin\theta$. On a wire: $\vec{F} = I\vec{L}\times\vec{B}$, magnitude $F = BIL\sin\theta$.

9. What is the magnetic field magnitude at distance $r$ from a long straight current-carrying wire?

   $B = \frac{\mu_{0}I}{2\pi r}$, where $\mu_{0} = 4\pi\times10^{-7}\ \text{T·m/A}$. Field lines form concentric circles given by the right-hand rule.

10. State Faraday's law of electromagnetic induction.

    The induced EMF equals the negative rate of change of magnetic flux: $\varepsilon = -N\frac{d\Phi_{B}}{dt}$, where flux $\Phi_{B} = BA\cos\theta$.

11. State Lenz's law.

    An induced current flows in the direction that opposes the change in magnetic flux producing it. This is the source of the negative sign in Faraday's law and reflects energy conservation.

12. Relate wave speed, frequency, and wavelength; define period.

    $v = f\lambda$. Period is the time for one cycle: $T = \frac{1}{f}$. Frequency $f$ is measured in hertz (cycles per second).

13. Compare transverse and longitudinal waves with examples.

    In transverse waves the oscillation is perpendicular to propagation (e.g., light, waves on a string). In longitudinal waves the oscillation is parallel to propagation (e.g., sound, compression waves).

14. What are the resonant frequencies of a string (or pipe open at both ends) of length $L$?

    $f_{n} = \frac{nv}{2L}$ for $n = 1, 2, 3, \ldots$, where $n=1$ is the fundamental. Harmonics are integer multiples of the fundamental.

15. Give the resonant frequencies of a pipe closed at one end.

    $f_{n} = \frac{nv}{4L}$ for odd $n = 1, 3, 5, \ldots$ only. Even harmonics are absent because of the fixed-end/open-end boundary conditions.

16. State the equation for the Doppler effect in sound.

    $f' = f\left(\frac{v \pm v_{observer}}{v \mp v_{source}}\right)$. Signs are chosen so that relative approach raises the observed frequency and recession lowers it.

17. Define sound intensity level in decibels.

    $\beta = 10\log_{10}\left(\frac{I}{I_{0}}\right)$ dB, where $I_{0} = 10^{-12}\ \text{W/m}^{2}$ is the threshold of hearing. Intensity itself falls off as $I \propto \frac{1}{r^{2}}$.

18. State the law of reflection and Snell's law of refraction.

    Reflection: angle of incidence equals angle of reflection, $\theta_{i} = \theta_{r}$. Refraction (Snell's law): $n_{1}\sin\theta_{1} = n_{2}\sin\theta_{2}$, with index $n = \frac{c}{v}$.

19. State the thin-lens/mirror equation and the magnification formula.

    $\frac{1}{f} = \frac{1}{d_{o}} + \frac{1}{d_{i}}$. Magnification: $m = \frac{h_{i}}{h_{o}} = -\frac{d_{i}}{d_{o}}$. Positive $m$ is upright; negative $m$ is inverted.

20. Define the critical angle for total internal reflection.

    Total internal reflection occurs when light travels from a denser to a rarer medium ($n_{1} > n_{2}$) at angles beyond $\theta_{c}$, where $\sin\theta_{c} = \frac{n_{2}}{n_{1}}$.

21. State the double-slit condition for constructive interference of light.

    Bright fringes (constructive interference) occur when the path difference equals an integer number of wavelengths: $d\sin\theta = m\lambda$, $m = 0, 1, 2, \ldots$. Destructive: $d\sin\theta = (m+\tfrac{1}{2})\lambda$.

22. State the first law of thermodynamics.

    $\Delta U = Q - W$, where $\Delta U$ is the change in internal energy, $Q$ is heat added to the system, and $W$ is work done by the system. It expresses energy conservation.

23. State the second law of thermodynamics and define entropy change.

    The total entropy of an isolated system never decreases: $\Delta S_{universe} \geq 0$. For a reversible process, $\Delta S = \frac{Q_{rev}}{T}$. Heat flows spontaneously from hot to cold.

24. Give the equations for heat causing temperature change versus phase change.

    Temperature change: $Q = mc\Delta T$, where $c$ is specific heat. Phase change (constant temperature): $Q = mL$, where $L$ is the latent heat of fusion or vaporization.

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