Comprehensive notes for Chapter 14 Current Electricity. Covers Electric Current, Ohm's Law, Resistance, Combination of Resistors, Electrical Energy, Joule's Law, and House Wiring.
Definition: The time rate of flow of electric charge through any cross section is called electric current.
I = Q/t
Unit: Ampere (A). $1A = 1C/1s$.
Measurement: measured by Ammeter (connected in series) or detected by Galvanometer (series).
Potential Difference (V): The energy dissipated as unit charge moves from one point to another in a circuit. $V = W/Q$. Unit: Volt ($1V = 1J/C$). Measured by Voltmeter (connected in parallel).
Electromotive Force (EMF): The total energy supplied by a battery/cell to a unit positive charge as it flows through the whole closed circuit (including inside the battery). Source transforms non-electrical energy to electrical energy.
The current passing through a conductor is directly proportional to the potential difference applied across its ends, provided the temperature and physical state of the conductor do not change.
V = IR
Resistance (R): Opposition to flow of current. Unit: Ohm ($\Omega$).
Factors affecting Resistance: Length ($R \propto L$), Area ($R \propto 1/A$). Specific Resistance ($\rho$): $R = \rho L/A$. Unit of $\rho$: $\Omega m$.
Joule's Law: Heat generated in a resistance due to current. $W = I^2Rt$ or $W = VIt$. Unit: Joule.
Electric Power (P): Rate of doing work. $P = W/t = VI = I^2R = V^2/R$. Unit: Watt (W).
Kilowatt-Hour (kWh): Commercial unit of electrical energy. Energy consumed by 1000W appliance in 1 hour. $1 kWh = 3.6 MJ$. (1 Unit).