Electricity
Physics Formulas & Circuit Laws
Current is the rate of flow of electric charge through a conductor.
↔ Swipe to view formulasCharge (Q): $$Q = ne$$
($e = 1.6 \times 10^{-19} \text{ C}$, $n$ = number of electrons)
Current (I): $$I = \frac{Q}{t}$$
(Unit: Ampere (A) = Coulomb/Second)
Potential difference ($V$) is the work done to move a unit charge.
Potential Difference (V): $$V = \frac{W}{Q}$$
Ohm’s Law: $$V = IR$$
(At constant temperature, $V \propto I$)
Resistance ($R$) depends on the length, area, and material of the conductor.
Formula: $$R = \rho \frac{l}{A}$$
Resistivity ($\rho$): $$\rho = \frac{R \cdot A}{l}$$
(Unit: $\Omega \cdot m$)
Effective resistance for different arrangements of resistors.
In Series: $$R_s = R_1 + R_2 + R_3 + …$$
(Current remains same, Voltage divides)
In Parallel: $$\frac{1}{R_p} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3} + …$$
(Voltage remains same, Current divides)
Work done by electric current is converted into heat energy.
Joule’s Law of Heating (H): $$H = I^2 Rt = VIt = \frac{V^2}{R}t$$
Electric Power (P): $$P = \frac{W}{t} = VI = I^2 R = \frac{V^2}{R}$$
Commercial Unit of Energy: $$1 \text{ kWh} = 3.6 \times 10^6 \text{ J}$$