Electronics Information
Electronics Information tests voltage, current, resistance, power, circuit rules, and common components. Voltage is electrical pressure, current is charge flow, and resistance opposes current.
Ohm's law and power
Ohm's law is V = IR. Power is P = VI, which also gives P = I²R and P = V²/R. Use the form that matches the known values. In a series circuit, current is the same through each component; voltages add; resistances add. In a parallel circuit, voltage is the same across each branch; currents add; total resistance is less than the smallest branch resistance.
Meters and components
An ammeter measures current and is connected in series. A voltmeter measures voltage and is connected in parallel. Resistor color-code digits run black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, gray 8, white 9; gold means ±5 percent and silver ±10 percent.
Worked example
A 12 V source is connected across a 4 Ω resistor. I = V/R = 12/4 = 3 A. Power = VI = 12 × 3 = 36 W. As a check, I²R = 9 × 4 = 36 W. If two such resistors were in parallel across the same source, each branch would carry 3 A, the total current would be 6 A, and the equivalent resistance would be 2 Ω.
Traps
Do not mix series and parallel rules. Connecting an ammeter in parallel or a voltmeter in series gives wrong readings and can damage equipment. Current is not used up by resistors. Check whether a question asks for total or branch values.