What the board asks
We went through the ISC board papers, question by question, and matched each question to a topic. Here is what was asked, how often, and what was never asked.
Physics: 427 topics in the 2027 syllabus, across 9 units. The board has asked 269 of them at least once. 158 were never asked in the papers we checked.
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P9 Electronic Devices
All the topics in Physics: Electronic Devices
Asked topics first, the most asked at the top. Tap a topic to see what to write, the result, the years, and the real board questions.
27 topics shown
| # | Topic | Type | Marks | Times asked | Last asked | Status |
|---|---|---|---|---|---|---|
| 1 | Doping, n-type and p-type, donors, acceptors, carriersDefine doping and extrinsic semiconductor; for n-type name the pentavalent (donor) impurities and for p-type the trivalent (acceptor) impurities, explain with a bond sketch how each gives a free electron or a hole, and name the majority and minority carriers in each type. | Statement | 1 | 6 papers | 2026 | Asked |
| 2 | Distinguish conductors, semiconductors, insulators by energy bands (table)Draw a table comparing the three on forbidden gap, state of the valence and conduction bands at room temperature, conductivity, effect of temperature, and two examples each, and quote the energy gaps of carbon (diamond), silicon and germanium in eV. | Comparison | 1 | 5 papers | Specimen 2027 | Asked |
| 3 | Give reason: semiconductor resistance falls as temperature risesExplain in two or three lines, using covalent bonds and the band gap, why the conductivity of a semiconductor increases (resistance decreases) when it is heated, and contrast this with a metal, whose resistance increases. | Give reason | 1 | 3 papers | Specimen 2027 | Asked |
| 4 | Forward and reverse biasing: circuits and effectsDefine forward bias and reverse bias, draw the two battery connections, and for each state what happens to the width of the depletion layer, the height of the potential barrier, the resistance of the junction, and which carriers carry the current. | Diagram | 1 | 3 papers | Specimen 2027 | Asked |
| 5 | p-n junction: depletion region, potential barrier, diode symbolExplain how diffusion of majority carriers across a p-n junction and their recombination leave a layer of immobile ions, define depletion region and potential barrier, draw the junction showing the ions and the direction of the barrier field, and draw the symbol of a junction diode marking the p side and the n side. | Statement | 1 | 3 papers | 2026 | Asked |
| 6 | Half wave rectifier: circuit, working, input and output waveformsDraw the labelled circuit (ac mains, transformer, one diode, load resistor with the output across it), explain what the diode does in the positive and in the negative half cycle of the input, and draw the input and output voltage waveforms one below the other on the same time scale. | Device | 3 | 3 papers | 2026 | Asked |
| 7 | Zener diode as a voltage regulator: circuit and workingDraw the labelled circuit (unregulated dc input, series resistor R_S, Zener diode in reverse bias in parallel with the load R_L), and explain how the output stays at V_Z when the input voltage rises or falls and when the load current changes. | Device | 3 | 3 papers | 2025 | Asked |
| 8 | Give reasons: extrinsic semiconductors and their usefulnessAnswer in one or two lines each: why doping raises conductivity; why a doped crystal is still neutral; why extrinsic semiconductors are useful although they are neither good nor bad conductors; and one advantage of semiconductor devices over the older bulky electronic devices. | Give reason | 1 | 2 papers | Specimen 2027 | Asked |
| 9 | Give reasons: behaviour of a junction diode under biasAnswer in one or two lines each: why the reverse current is extremely small and almost independent of the voltage; why it increases with temperature; why a forward-biased diode has low resistance; why the depletion region has no free carriers; why a diode can be used as a rectifier. | Give reason | 1 | 2 papers | Specimen 2027 | Asked |
| 10 | V-I characteristics of a junction diode, with circuitDraw the circuit used to study the characteristics (potential divider, voltmeter across the diode, milliammeter in forward bias and microammeter in reverse bias), then draw the labelled forward and reverse curves on one graph, marking knee voltage, reverse saturation current and breakdown voltage, with current in mA on the forward side and microampere on the reverse side. | Graph | 2 | 2 papers | 2026 | Asked |
| 11 | Zener diode: definition, symbol and V-I characteristicsDefine a Zener diode, draw its symbol, and draw its V-I characteristic showing a forward curve like an ordinary diode and, in reverse bias, a sharp breakdown at the Zener voltage after which the voltage stays almost constant while the current changes; mark V_Z. | Graph | 2 | 2 papers | 2026 | Asked |
| 12 | Rectifier: function, principle, role of each componentState what a rectifier does and the property of a diode it depends on, then write one line on the function of each part of a rectifier circuit: the transformer, the centre tap, the diode(s) and the load resistor. | Statement | 1 | 2 papers | 2025 improvement | Asked |
| 13 | Full wave rectifier (centre tap, two diodes): circuit, working, waveformsDraw the labelled circuit (centre-tapped transformer, two diodes, load resistor between the centre tap and the joined diode ends), explain which diode conducts in each half cycle and why the current through the load is in the same direction both times, and draw the input and output voltage waveforms against time. | Device | 3 | 2 papers | 2025 | Asked |
| 14 | Solar cell: definition, working, energy conversionDefine a solar cell, draw its simple structure (thin p layer over an n layer with metal contacts) and symbol, explain its working in three steps (light creates electron-hole pairs near the junction; the junction field separates them; charges collect on the two sides giving an emf that drives current through a load), and give two uses. | Device | 2 | 1 paper | Specimen 2027 | Asked |
| 15 | Compare intrinsic with extrinsic, n-type with p-type (table)Write two short tables: intrinsic against extrinsic (purity, number of electrons and holes, conductivity, dependence on temperature) and n-type against p-type (impurity valency and name, majority carrier, minority carrier, position of the impurity level). | Comparison | 1 | 1 paper | 2025 | Asked |
| 16 | LED: symbol, forward bias, working, energy conversionDraw the symbol of an LED and its circuit (forward biased, with a series resistor), explain in brief that electrons and holes recombine at the junction and the energy released comes out as light, state the energy change, say what decides the colour, and give two uses. | Device | 2 | 1 paper | 2025 improvement | Asked |
| 17 | Compare LED, photodiode, solar cell, Zener diode (table)Draw a table for the four special diodes giving symbol, biasing used (forward, reverse, none, reverse breakdown), energy change or action, and one use each. | Comparison | 2 | 1 paper | 2025 | Asked |
| 18 | Band formation; define valence, conduction and forbidden bandsExplain in a few lines how the sharp levels (1s, 2s, 2p, 3s ...) of an isolated atom such as copper spread into bands of very closely spaced levels when a very large number of atoms come together to form the solid, then define energy band, valence band, conduction band and forbidden band (energy gap, in eV), and say in two lines how the free electrons of a metal carry current. | Statement | 1 | 1 paper | 2023 | Asked |
| 19 | Importance of LEDs: advantages over filament bulbsWrite three or four advantages of LED lamps over filament bulbs and say in one line why they matter for the environment. | Give reason | 1 | 1 paper | 2020 | Asked |
| 20 | Energy band diagrams: conductor, semiconductor, insulatorDraw three separate labelled energy band diagrams: a conductor (valence and conduction bands overlapping, or conduction band partly filled, no forbidden band), a semiconductor (small gap of about 1 eV, valence band full and conduction band empty at 0 K) and an insulator (large gap, more than about 3 eV), marking conduction band, valence band and Eg on each. | Diagram | 3 | 1 paper | 2018 | Asked |
| 21 | Numericals: diode resistance from the V-I characteristicFrom a given forward characteristic (graph or pairs of readings) compute the resistance at a stated point as V/I, and the dynamic resistance as the ratio of a small change in voltage to the change in current, converting mA to A. | Numericals | 2 | 1 paper | 2018 | Asked |
| 22 | Intrinsic semiconductor: electrons, holes, electron-hole pairsDescribe pure Si or Ge (four valence electrons, four covalent bonds), how thermal energy breaks a bond to give a free electron and a hole, define a hole and say how it moves, state that electrons and holes are equal in number in a pure semiconductor and that both carry current, and draw the band diagram of an intrinsic semiconductor above 0 K (a few electrons in the conduction band, equal holes in the valence band). | Statement | 2 | never | Never asked | |
| 23 | Energy band diagrams: intrinsic, n-type, p-type semiconductorsDraw three labelled band diagrams: intrinsic (equal electrons and holes), n-type (donor level just below the conduction band, many electrons in the conduction band) and p-type (acceptor level just above the valence band, many holes in the valence band). | Diagram | 2 | never | Never asked | |
| 24 | Numericals: current in simple diode circuitsFor a circuit of a battery, resistor(s) and one or two diodes, decide from the polarity whether each diode is forward or reverse biased, replace a forward-biased diode by a closed switch (or by its stated drop of 0.7 V or 0.3 V, or its stated forward resistance) and a reverse-biased diode by an open switch, then compute the current and the p.d. across the resistor. | Numericals | 2 | never | Never asked | |
| 25 | Compare half wave and full wave rectifiers; predict outputsDraw a table comparing the two on number of diodes, need for a centre tap, part of the input cycle used, output waveform and output frequency, and say what the output becomes if one diode of a full wave rectifier is removed or the diode of a half wave rectifier is reversed. | Comparison | 2 | never | Never asked | |
| 26 | Photodiode: symbol, reverse bias circuit, working, useDraw the symbol of a photodiode and its circuit (reverse biased, light falling on the junction), explain that photons of energy more than the band gap create electron-hole pairs so the reverse current increases with light intensity, say why it is used in reverse bias, and give two uses. | Device | 2 | never | Never asked | |
| 27 | Numericals: Zener regulator currents and series resistorFor a Zener regulator with given input voltage, Zener voltage, series resistor and load, compute the load current, the current through the series resistor, the Zener current, and the series resistor needed for a given Zener current. | Numericals | 2 | never | Not in syllabus |
This list was made from the 2027 syllabus and checked with 9 board papers, including the 2027 specimen paper. It is not yet checked with the textbook.
The 10 topics Physics papers ask most
Counted on the board papers from 2018 to the 2027 specimen paper, which every unit has been checked against.
- 1.Numericals: peak, rms, mean, frequency from an ac equationP4 Electromagnetic Induction and Alternating Currents · asked 7 times since 2018
- 2.Uses and special properties of each region (table)P5 Electromagnetic Waves · asked 7 times since 2018
- 3.State Bohr's postulates for the hydrogen atomP8 Atoms and Nuclei · asked 7 times since 2018
- 4.Magnetic force on a moving charge and Lorentz forceP3 Magnetic Effects of Current and Magnetism · asked 6 times since 2018
- 5.Numericals: average power and power factorP4 Electromagnetic Induction and Alternating Currents · asked 6 times since 2018
- 6.Doping, n-type and p-type, donors, acceptors, carriersP9 Electronic Devices · asked 6 times since 2018
- 7.Numericals: two-loop network with two batteries (Kirchhoff)P2 Current Electricity · asked 5 times since 2018
- 8.Derive B at the centre of a circular loopP3 Magnetic Effects of Current and Magnetism · asked 5 times since 2018
- 9.Numericals: B at the centre of a circular coilP3 Magnetic Effects of Current and Magnetism · asked 5 times since 2018
- 10.Ampere's law: derive B near a long straight wireP3 Magnetic Effects of Current and Magnetism · asked 5 times since 2018