Electrical and Electronic Engineering
Scope
Electrical and Electronic Engineering tests circuit laws, power, semiconductor devices, digital logic, and electrical safety. Questions often require series-parallel simplification, current or voltage calculation, or safe isolation practice.
Core rules
- Ohm's law: V = I x R. Power: P = V x I = I2R = V2/R.
- In series, current is the same and voltages add; in parallel, voltage is the same and currents add.
- Equivalent parallel resistance for two resistors is R1R2/(R1+R2); for equal resistors, divide by the number of branches.
- AC RMS values are used for normal power calculations; peak value is larger than RMS for a sine wave.
- Electrical safety requires isolation, lockout, testing for dead, and protective earthing.
Worked example
A 12 V source connects a 4 ohm resistor in series with a parallel pair of 6 ohm and 3 ohm resistors. Parallel equivalent = 6 x 3 / (6 + 3) = 2 ohms. Total resistance = 4 + 2 = 6 ohms. Current = 12 / 6 = 2 A. Voltage across the parallel pair = 2 x 2 = 4 V; voltage across the 4 ohm resistor = 2 x 4 = 8 V. Reasoning: simplify the parallel section, add series resistance, then use Ohm's law.
Traps
Adding parallel resistances directly is wrong. Confusing series and parallel rules reverses current and voltage conclusions. Using peak voltage as RMS overstates power. Working live without lockout is a serious safety violation.