Basic Electrical and Electronic Fundamentals
This domain tests the language of circuits: charge, current, voltage, resistance, Ohm’s law, power, and the two basic connection patterns. Expect numerical questions that mix unit prefixes with series and parallel rules.
Core rules
- Current is rate of charge flow, I = Q/t, in amperes; voltage is energy per charge, V = W/Q, in volts; resistance opposes current, in ohms.
- Ohm’s law: V = IR. Power: P = VI = I²R = V²/R.
- Series: one path, same current, voltages add, R_eq = R1 + R2 + …
- Parallel: same voltage, branch currents add, 1/R_eq = 1/R1 + 1/R2 + …
Worked example
A 12 V battery feeds 4 Ω and 6 Ω in series. Total resistance is 10 Ω, so I = 12/10 = 1.2 A. The 4 Ω drop is V = 1.2 × 4 = 4.8 V; the 6 Ω drop is 7.2 V; the drops add to 12 V. Total power is P = VI = 12 × 1.2 = 14.4 W, or I²R = 1.44 × 10 = 14.4 W. If the same resistors were in parallel, R_eq = (4 × 6)/(4 + 6) = 2.4 Ω and the battery current would be 5 A.
Traps
- Mixing mA and A, or kΩ and Ω, before substitution.
- Applying the voltage-divider rule to parallel branches.
- Forgetting that parallel resistance is always smaller than the smallest branch.
- Using total voltage with one branch resistance when calculating branch power.