Electronics Information
The core trio
Electronics Information tests voltage (E, electrical pressure), current (I, flow in amperes), and resistance (R, opposition in ohms), plus the components and safety practices built on them.
Laws and formulas
- Ohm's law: E = I x R.
- Power: P = I x E, and by substitution P = I^2 R = E^2 / R.
- Series circuits: resistances add, current is the same everywhere, voltage divides.
- Parallel circuits: voltage is the same across each branch, and currents add. For two resistors, R = (R1 x R2)/(R1 + R2).
- A capacitor stores charge and blocks DC while passing AC; an inductor opposes changes in current; a diode allows current one way; a transistor amplifies or switches.
Traps
- Adding parallel resistances as if they were in series. The total is always smaller than the smallest resistor.
- Confusing meters: an ammeter goes in series with the circuit, a voltmeter in parallel with the component.
- Forgetting the resistor color code order: black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, gray 8, white 9.
- Overlooking that a short circuit bypasses resistance and causes high current.
- Reversing AC and DC: DC flows one direction, AC reverses periodically.
Worked example
A 12-volt source is connected across a 4-ohm resistor. Current = E / R = 12 / 4 = 3 A. Power = I x E = 3 x 12 = 36 W. Check with P = E^2 / R = 144 / 4 = 36 W.
Rule of thumb
Draw the E-I-R triangle: cover the unknown and read the formula. Then check units, because answer choices often differ only in amps versus watts.