Electronics Information
Core relationships
Voltage (V, volts) is electrical pressure; current (I, amperes) is the flow; resistance (R, ohms) opposes it. Ohm's law: V = IR. Power: P = VI, and by substitution P = I squared times R, or V squared divided by R. Energy in watt-hours equals watts times hours.
Circuits
- Series: one path. Current is the same everywhere, voltage divides across the loads, and resistances add.
- Parallel: multiple paths. Voltage is the same across each branch, current divides, and total resistance is less than the smallest branch.
Components
A resistor limits current; a capacitor stores charge in an electric field; an inductor stores energy in a magnetic field; a diode allows current in one direction only; a transistor amplifies or switches; a transformer changes AC voltage; a fuse or breaker opens the circuit on overload. AC reverses direction (household current), DC flows one way (batteries). Copper, silver, and aluminum conduct; rubber, glass, and plastic insulate.
Traps
- Confusing power with energy; watt-hours, not watts, measure consumption.
- Reversing the series and parallel rules.
- Resistor color code order: black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, gray 8, white 9.
- Assuming a capacitor stores current rather than charge.
Worked example
A 12 V source across a 4 ohm resistor: I = V divided by R = 12 divided by 4 = 3 A. Power = V times I = 12 times 3 = 36 W.