PHY 2049 Exam 2 Flashcards

A set of practice flashcards for the PHY 2049 Exam 2 covering electricity, capacitance, and basic circuits.

Electric charge

Property of matter causing electric forces. Proton = $+1.6 \times 10^{-19}\,\text{C}$, Electron = $-1.6 \times 10^{-19}\,\text{C}$.

Like charges

Repel.

Opposite charges

Attract.

Coulomb's Law

$$F = \frac{k q_1 q_2}{r^2}$$

Electric field

$$E = \frac{F}{q} = \frac{k Q}{r^2}$$

Direction of E

Direction a positive test charge moves.

Parallel plate field

$$E = \frac{\sigma}{\epsilon_0}$$

Force in electric field

$$F = q E$$

Electric potential

$V = \frac{k Q}{r}$ (scalar, $\text{J/C}$)

Potential energy

$$U = \frac{k q_1 q_2}{r}$$

Work and PE

$$W = -\Delta U$$

Equipotential

No work done moving along one; $E$ is perpendicular.

Electric field inside conductor

Zero.

Excess charge on conductor

Resides on surface.

Capacitance

$$C = \frac{Q}{V}$$

Parallel plate capacitance

$$C = \frac{\epsilon_0 A}{d}$$

Capacitors in parallel

Add directly.

Capacitors in series

Add reciprocals.

Charge in series capacitors

Same.

Voltage in parallel capacitors

Same.

Capacitor energy

$$U = \frac{1}{2} C V^2$$

Current

$$I = \frac{dq}{dt}$$

Ohm's Law

$$V = I R$$

Resistance

$$R = \frac{\rho L}{A}$$

Resistors in series

Add directly.

Resistors in parallel

Add reciprocals.

Power

$$P = I V = I^2 R = \frac{V^2}{R}$$

Kirchhoff Junction Rule

Current in = Current out.

Kirchhoff Loop Rule

Sum of voltage changes around a loop = $0$.

Exam Tip

Point charge: use $E = \frac{k Q}{r^2}$. Parallel plates: use $E = \frac{\sigma}{\epsilon_0}$. Potential: $V = \frac{k Q}{r}$. Potential energy: $U = \frac{k q_1 q_2}{r}$.

Voltage in parallel capacitors

Same.