Board-style MCQs and past-paper numericals in the BIEK / Sindh Board pattern. Tap an option to check yourself instantly. Solved questions are at the bottom.
Multiple-choice questions
Solved numericals (past papers)
Diode forward current (Ohm's law in the circuit)
A silicon diode (forward drop 0.7 V) is in series with a 220 Ω resistor across a 5.0 V supply. Find the current.
Voltage across resistor = 5.0 − 0.7 = 4.3 V
I = V/R = 4.3 / 220 = 0.0195 A ≈ 19.5 mA
Series resistor for an LED
A red LED (drop 2.0 V, current 20 mA) runs from a 9.0 V battery. Find the series resistor needed.
Voltage across resistor = 9.0 − 2.0 = 7.0 V
R = V/I = 7.0 / (20 × 10⁻³) = 350 Ω
Transistor current gain β
In a transistor, the base current is 40 μA and the collector current is 4.0 mA. Find the current gain β.
β = I_C / I_B = (4.0 × 10⁻³) / (40 × 10⁻⁶)
= (4.0 × 10⁻³) / (4.0 × 10⁻⁵) = 100
Emitter current of a transistor
A transistor has I_B = 50 μA and I_C = 5.0 mA. Find the emitter current I_E.
I_E = I_C + I_B = 5.0 mA + 0.05 mA
= 5.05 mA
Reverse saturation (leakage) current
A reverse-biased diode passes 2.0 μA across a reverse voltage of 10 V. Find its reverse resistance.
R = V/I = 10 / (2.0 × 10⁻⁶)
= 5.0 × 10⁶ Ω = 5.0 MΩ
Ripple frequency of a full-wave rectifier
A full-wave rectifier is fed from a 50 Hz AC mains supply. Find the output ripple frequency.
For full-wave rectification the output ripple frequency = 2 × input frequency
f = 2 × 50 = 100 Hz (a half-wave rectifier would give 50 Hz)