Practise 27 real Federal Board questions on Electronics from 2023 to 2026. See the answer and explanation as soon as you answer.
Electronics is one of the 14 main chapters in our Federal Board FSC Physics question bank (11th and 12th class), and about 5% of its real questions come from it. Tayyari Karo has 27 real questions on this chapter from 2023 to 2026; 10 are multiple choice and marked instantly, and the rest are short and long questions with a model answer. By difficulty: 19 medium, 8 easy.
Work through the questions below, then open the explanation for each one. Redo the ones you missed a few days later.
These are real past-paper questions. Think of your answer first, then open the explanation.
A bridge rectifier is used to:
Answer: B. Convert AC to DC
A bridge rectifier (four diodes) converts alternating current into direct current using full-wave rectification.
A forward biased PN Junction offers:
Answer: B. Very low resistance
Forward biasing narrows the depletion region, allowing majority carriers to flow easily — very low resistance.
In forward biasing of a p-n junction diode, the potential barrier:
Answer: A. Decreases
Forward bias opposes the built-in field of the depletion region, reducing (though not fully eliminating) the potential barrier.
Conversion of A.C into D.C is called:
Answer: B. Rectification
Rectification is the process of converting alternating current into direct current, typically using diodes.
PN junction when reverse biased acts as:
Answer: C. Capacitor
In reverse bias the depletion region widens, acting as an insulating dielectric between the two conducting P and N regions — the junction behaves like a (voltage-dependent) capacitor, storing charge Q=CV.
A mercury volume of 1600×10⁻⁶ m³ is subjected to a pressure of 1.4×10⁶ Pa. If the bulk modulus of mercury is 2.8×10¹⁰ Pa, then the decrease in its volume is:
Answer: A. 8×10⁻⁸ m³
ΔV = PV/B = (1.4×10⁶ × 1600×10⁻⁶)/(2.8×10¹⁰) = 2240/(2.8×10¹⁰) = 8×10⁻⁸ m³.
Briefly explain light dependent resistor (LDR). Give one application.
A light dependent resistor (LDR) is a semiconductor device (made of a photoconductive material like cadmium sulphide) whose resistance decreases as the intensity of light falling on it increases — because more light generates more electron-hole pairs (charge carriers) in the material, increasing its conductivity.
Application: LDRs are used in automatic street-light circuits, which switch the lights on at dusk (when light intensity, and hence LDR resistance, is high) and off at dawn.
Why in a transistor is the base region made thin and lightly doped?
The base is made thin so that most of the charge carriers injected from the emitter can cross it quickly and reach the collector before they can recombine with the majority carriers of the base. It is made lightly doped so that it has relatively few majority carriers, further minimizing recombination in the base. Together these ensure that only a very small fraction of the emitter current flows out as base current, while the vast majority reaches the collector — giving the transistor its large current gain (β).
| Session | Questions |
|---|---|
| 2026 Annual | 5 |
| 2025 1st Annual | 4 |
| 2025 2nd Annual | 6 |
| 2024 Annual | 7 |
| 2023 Annual | 5 |
27 real Federal Board (FBISE) Physics questions on Electronics from 2023 to 2026, for 11th and 12th class. Each one shows the session it came from.
No. We could not find an official FBISE marking scheme for these papers, so the answers and explanations are written by Tayyari Karo for practice. Check anything important with your teacher or textbook.
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