Ohm's Law & Circuits
Build circuits with resistors, batteries, and ammeters. See current flow and voltage drops in real time.
Key Notes
Ohm's Law: V = IR — the voltage across a conductor is proportional to the current through it (for ohmic materials).
Resistance R = ρL/A, where ρ is resistivity, L is length, A is cross-section area.
Resistors in series: R_total = R₁ + R₂ + R₃ + ... (current is the same through each).
Resistors in parallel: 1/R_total = 1/R₁ + 1/R₂ + ... (voltage is the same across each).
Power dissipated: P = VI = I²R = V²/R. This is Joule's law of heating.
Kirchhoff's Current Law (KCL): The sum of currents entering a junction equals the sum leaving it.
Kirchhoff's Voltage Law (KVL): The sum of potential differences around any closed loop is zero.
Internal resistance of a battery: V_terminal = EMF − Ir, where r is internal resistance.
Formulas
Ohm's Law
Voltage = Current × Resistance.
Resistance
Depends on material (ρ), length (L), and area (A).
Series Resistance
Equivalent resistance in series.
Parallel Resistance
Equivalent resistance in parallel.
Power
Electrical power dissipated.
Terminal Voltage
Voltage across battery terminals under load.
Important Points
Not all materials follow Ohm's law (e.g., diodes, LEDs). These are called non-ohmic.
In series, the largest resistor gets the most voltage (V = IR, same I).
In parallel, the smallest resistor carries the most current (I = V/R, same V).
When a cell is short-circuited, I = EMF/r (maximum current, dangerous!).
Wheatstone bridge is balanced when R₁/R₂ = R₃/R₄ — no current through the galvanometer.
Temperature increases resistance in metals (positive temperature coefficient) but decreases it in semiconductors.
Ohm's Law & Circuits notes from sciphylab (also known as SciPhy, SciPhy Lab, SciPhy Labs, Physics Lab). Class 12 physics revision for JEE Mains, JEE Advanced, NEET UG, AP Physics 1/2/C, SAT, and CUET-UG.