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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P4 Electromagnetic Induction and Alternating Currents

All the topics in Physics: Electromagnetic Induction and Alternating Currents

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.

74 topics shown

#	Topic	Type	Marks	Times asked	Last asked	Status
1	Numericals: peak, rms, mean, frequency from an ac equationFrom e = e0 sin(omega t) (or an i-t graph) read the peak value and omega, then find frequency, period, rms and mean values, and the peak or rms current through a resistor; convert rms to peak and back.	Numericals	1	7 papers	Specimen 2027	Asked
2	Numericals: average power and power factorCalculate the average power consumed from peak or rms values and the phase angle (or from I_rms^2 R), the power factor from R and Z or from the phase angle, and the phase angle from a given power factor.	Numericals	2	6 papers	Specimen 2027	Asked
3	Numericals: motional emf of a moving rod or axleCalculate the emf across a rod, axle or wire moving at right angles to a field, including cases where the speed is given in km/h or must be found by differentiating a displacement-time relation.	Numericals	2	3 papers	Specimen 2027	Asked
4	Numericals: reactance and current for single R, L or CCalculate X_L or X_C at a given frequency (or from peak voltage and peak current), then the rms and peak current when the element alone is connected to an ac source; find L or C from a known reactance.	Numericals	1	3 papers	Specimen 2027	Asked
5	Motional emf: meaning and factors it depends onSay what motional emf is (the emf induced across a conductor moving so as to cut magnetic field lines) and state the factors it depends on: flux density B, length l of the conductor, speed v, and the angle between the motion and the field.	Statement	2	3 papers	2026	Asked
6	Give reasons: laminated core, soft-iron coreAnswer in one or two lines each: why the core is laminated (to reduce eddy currents and their heating) and why it is made of soft iron and not steel (narrow hysteresis loop, low coercive force, so little energy lost per cycle of magnetisation; high permeability).	Give reason	1	3 papers	2026	Asked
7	Numericals: self-inductance from induced emfUse e = L dI/dt to find L, the induced emf or the rate of change of current when the current in a coil changes by a given amount in a given time; also flux linkage from N phi = L I.	Numericals	2	3 papers	2025 improvement	Asked
8	Numericals: ideal transformer turns, voltages and currentsFrom any three of Np, Ns, Ep, Es find the fourth and the turns ratio; find the secondary (or primary) current for an ideal transformer and state the assumption used.	Numericals	2	3 papers	2025 improvement	Asked
9	Give reasons: currents and voltages in an ideal transformerExplain in two or three lines: why the current in the low-voltage winding is larger, which winding of a step-up or step-down transformer carries more current, why a transformer does not create energy, and why it cannot work on a steady dc supply.	Give reason	1	3 papers	2025 improvement	Asked
10	Numericals: series LR circuit or coil with resistanceFor a coil of given L and R (or a separate L and R in series) on an ac supply, calculate the reactance, impedance, rms current, the phase difference between voltage and current and the power factor.	Numericals	3	3 papers	2025 improvement	Asked
11	Numericals: series LCR impedance, current, phase, element voltagesFor given R, L, C and supply (as rms voltage and frequency, or as e = e0 sin(omega t)), calculate X_L, X_C, the impedance, the peak or rms current, the phase difference between current and supply voltage (saying which leads), and the pd across each element.	Numericals	3	3 papers	2023	Asked
12	Step-up versus step-down transformer, with where each is usedCompare the two types on turns ratio, voltage, current and thickness of winding wire, and name where each is used (step-up at the generating station; step-down at the city sub-station, in a phone charger, a doorbell).	Comparison	1	2 papers	Specimen 2027	Asked
13	Identify R, L or C from phase lead or lagFrom a pair of equations for e and i, or from an I-t graph drawn against a sine emf, decide whether the current is in phase with, leads or lags the voltage and so name the device or the unknown series component, with the reason.	Give reason	1	2 papers	Specimen 2027	Asked
14	Numericals: magnetic flux through a coil or circuitCompute the flux through a coil of N turns for a given B, area and orientation, and write the flux linked with a rod-and-rails circuit in symbols (B l x).	Numericals	1	2 papers	2025 improvement	Asked
15	Numericals: phase and impedance from e and i equationsGiven equations for the applied emf and the current, write the phase difference and which quantity leads, the impedance as e0/i0, the resistance and reactance of the circuit, and whether it is inductive or capacitive.	Numericals	2	2 papers	2025	Asked
16	Graph of impedance Z versus frequency for series LCRDraw a labelled graph of Z against f for a series LCR circuit: Z falls to its minimum value R at the resonant frequency f0 and rises on both sides; mark f0 and Z = R.	Graph	2	2 papers	2024	Asked
17	Find the direction of induced current using Lenz's lawFor a given picture (magnet moving towards or away from a coil, a coil moved towards a current-carrying coil, a loop entering or leaving a field, a current in a nearby circuit increasing or decreasing) decide whether the flux is increasing or decreasing, give the direction of the opposing field, and state the induced current as clockwise or anticlockwise for the stated observer.	Give reason	1	1 paper	Specimen 2027	Asked
18	Explain back emf effects: spark at switch, slow current growthExplain, using 'induced emf opposes the change', why a spark appears at a switch when an inductive circuit is broken, why the current in a coil takes time to grow and to die, and why self-inductance is called electrical inertia.	Give reason	2	1 paper	Specimen 2027	Asked
19	Explain use of transformers in long-distance power transmissionExplain why power is sent at high voltage (for the same power the current is small, so the I^2 R loss and the voltage drop in the lines are small), where step-up and step-down transformers are placed between the generating station and the home, and why this makes ac the choice for supply.	Give reason	2	1 paper	Specimen 2027	Asked
20	Draw one labelled cycle of ac current versus timeFrom an emf equation and the circuit, work out the peak value and the period, then draw one cycle against time with both axes labelled with units, the peak values and the times T/4, T/2, 3T/4, T marked; and read peak, period and frequency off a given graph.	Graph	2	1 paper	Specimen 2027	Asked
21	Why ac is preferred to dc; its drawbacksGive the reasons ac is used for supply (it can be stepped up or down with a transformer, so it is transmitted at high voltage with little loss; it is easy to generate and to control with a choke) and one or two drawbacks (more dangerous at the same rated voltage because the peak is higher; cannot be used directly for electroplating or charging).	Give reason	1	1 paper	Specimen 2027	Asked
22	Numericals: self-inductance of a solenoid from its dimensionsCalculate L of an air-cored or iron-cored solenoid from its number of turns (or turns in a given length), length and cross-section area.	Numericals	2	1 paper	2026	Asked
23	Give reasons: how L and C respond to ac, dcExplain in two or three lines each: why a coil passes less current on ac than on dc of the same voltage, why a capacitor blocks dc but passes ac, and how the brightness of a lamp in series with an inductor or a capacitor changes when the frequency is raised or an iron core is pushed into the coil.	Give reason	1	1 paper	2026	Asked
24	Numericals: coil on dc then ac, find R and LFrom the current a coil takes on a dc supply find its resistance, from the smaller current on an ac supply of the same voltage find its impedance, then the reactance and the self-inductance.	Numericals	3	1 paper	2026	Asked
25	State Lenz's law; name the law for current directionState Lenz's law in one sentence and say that it gives the direction of the induced current (it is the minus sign in e = -dphi/dt).	Statement	1	1 paper	2025	Asked
26	Derive motional emf e = Blv and power (Blv)^2/RFor a rod of length l sliding with velocity v on rails in a perpendicular field B: write the flux linked (B l x), differentiate to get the emf, then the current, the retarding force on the rod and the power the external agent must supply, showing it equals the heat produced in R.	Derivation	3	1 paper	2025 improvement	Asked
27	Numericals: current, force and power for rod on railsFor a rod of resistance R (or rails closed by R) moving at constant speed in a field, calculate the induced current, the force needed to keep it moving and the power spent or dissipated.	Numericals	2	1 paper	2025 improvement	Asked
28	Self-induction and self-inductance: definitions, henry, dimensionsDefine self-induction, define the coefficient of self-inductance both ways (flux linkage per unit current, and induced emf per unit rate of change of current), define one henry, give its equivalent units and dimensions, and name the phenomenon when a changing current in a coil induces an emf in the same coil.	Statement	2	1 paper	2024	Asked
29	Differences between ac and dc (table)Tabulate three or four differences: direction and magnitude with time, frequency (50 Hz against zero), whether it can be stepped up or down by a transformer, behaviour with an inductor and a capacitor, source (generator against cell), and loss in long-distance transmission.	Comparison	1	1 paper	2024	Asked
30	Show that a changing magnetic field produces a currentDescribe one experiment (bar magnet moved into and out of a coil joined to a galvanometer, or a current switched on and off in a neighbouring coil) with a sketch, state what the galvanometer shows in each case, and conclude that a current is induced only while the flux through the coil is changing.	Give reason	2	1 paper	2023	Asked
31	Numericals: mutual inductance from induced emf or fluxFind M, the emf induced in the second coil, or the flux linked with it, when the current in the first coil changes by a given amount in a given time.	Numericals	2	1 paper	2020	Asked
32	Obtain the resonant frequency of a series LCR circuitSet X_L = X_C at resonance, solve for the angular frequency and hence the frequency.	Derivation	2	1 paper	2020	Asked
33	Graphs of X_L and X_C versus frequencyDraw labelled graphs of inductive reactance against frequency (straight line through the origin, slope 2 pi L) and capacitive reactance against frequency (falling curve, a rectangular hyperbola).	Graph	2	1 paper	2019	Asked
34	Power factor; power absorbed and dissipated; special casesDefine power factor, give cos phi = R/Z, state its value and the average power for a pure resistor, a pure inductor, a pure capacitor and an LCR circuit at resonance, and say that only the resistance dissipates power while L and C absorb and return energy each quarter cycle.	Statement	1	1 paper	2019	Asked
35	Series resonance: condition and characteristicsDefine electrical resonance in a series LCR circuit and state its characteristics: X_L = X_C, impedance minimum and equal to R, current maximum (V/R), current in phase with voltage (power factor 1), power delivered by the source maximum, V_L and V_C equal and opposite.	Statement	2	1 paper	2019	Asked
36	Give reasons: eddy-current effects and laminationAnswer 'why' questions in two or three lines each: why a transformer or generator core is laminated, why a metal plate swinging between magnet poles stops quickly and why slots cut in it reduce the damping, why a galvanometer coil is wound on a metal frame.	Give reason	1	1 paper	2018	Asked
37	Numericals: series RC circuit (X_C, Z, current, C)For R and C in series on an ac supply, use the given phase angle or the component values to find the capacitive reactance, impedance and current, and the capacitance from X_C and the frequency.	Numericals	5	1 paper	2018	Asked
38	Numericals: resonant frequency, current and power at resonanceCalculate the resonant frequency of a given L and C, the L or C needed to resonate at a given frequency, and the impedance, current, power and power factor at resonance.	Numericals	2	1 paper	2018	Asked
39	Magnetic flux and electromagnetic induction: definitions, unitsDefine magnetic flux (with phi = B.A = BA cos theta, SI unit weber, dimensions, scalar nature), electromagnetic induction, induced emf and induced current, and list the three ways of changing the flux through a coil (change B, change area, change orientation).	Statement	1	never		Never asked
40	State Faraday's laws of electromagnetic inductionState both laws in words (an emf is induced whenever the flux linked with a circuit changes and lasts only while it changes; its magnitude equals the rate of change of flux linkage) and write the equation for a coil of N turns with the meaning of the minus sign.	Statement	2	never		Never asked
41	Numericals: induced emf and current from changing fluxFind the induced emf (and the current for a given resistance) when the flux through a coil changes: flux given as a function of time (differentiate), B changing at a steady rate, or the coil turned or pulled out of the field in a given time.	Numericals	2	never		Never asked
42	Explain Lenz's law as conservation of energyUsing a magnet pushed towards a coil, argue that the induced current must oppose the motion: work done against the repulsion becomes the electrical energy of the induced current; if it aided the motion, energy would be created from nothing.	Give reason	2	never		Never asked
43	Eddy currents: meaning, cause, effects and usesSay what eddy currents are (circulating currents induced in the body of a metal when the flux through it changes), why they heat the metal and oppose its motion (Lenz's law), name two or three uses (induction furnace, electromagnetic damping in a galvanometer, magnetic brakes, speedometer or energy meter) and the harm they do in iron cores.	Statement	2	never		Never asked
44	Mutual induction and mutual inductance: definitions, henryDefine mutual induction, define the coefficient of mutual inductance both ways (flux linked with the secondary per unit primary current, and emf induced in the secondary per unit rate of change of primary current), give its SI unit and the factors it depends on.	Statement	2	never		Never asked
45	Numericals: mutual inductance of coaxial solenoids from dimensionsCalculate M for two coaxial solenoids (or a short coil wound over a long solenoid) from the turns, length and area, and then the emf induced in one for a given rate of change of current in the other.	Numericals	2	never		Never asked
46	Transformer: labelled diagram, principle, working, turns-ratio theoryDraw a labelled transformer (laminated soft-iron core, primary and secondary windings, ac input, load), state the principle (mutual induction), explain the working, and obtain the voltage and current ratios for an ideal transformer; add two uses.	Device	3	never		Never asked
47	Numericals: transformer efficiency and input/output powerCalculate the efficiency of a real transformer from input and output voltages and currents, or use a given efficiency to find the output power, the secondary current or the primary current.	Numericals	2	never		Never asked
48	Transformer energy losses: cause and remedy (table)Tabulate the four losses with cause and remedy: copper loss (I^2 R heating of windings; thick low-resistance wire), eddy-current or iron loss (laminated core), hysteresis loss (soft iron or silicon steel core with a narrow B-H loop), flux leakage (windings one over the other on a closed core).	Comparison	2	never		Never asked
49	Numericals: power loss in a transmission lineFor a given power sent over a line of given resistance, find the line current, the power wasted as heat and the percentage loss at two different transmission voltages, and compare.	Numericals	2	never		Never asked
50	AC terms: peak, mean, rms, period, frequency, phaseDefine alternating current and emf, write e = e0 sin(omega t), and define instantaneous value, peak value, time period, frequency, angular frequency, phase and phase difference, mean (average) value and rms (effective) value, stating how mean and rms values are related to the peak value.	Statement	2	never		Never asked
51	Obtain the mean value of ac over half a cycleIntegrate I = I0 sin(omega t) over half a period and divide by T/2 to get the mean value; show that the mean over a full cycle is zero; write the same result for voltage.	Derivation	2	never		Never asked
52	Obtain the rms value of ac: I_rms = I0/sqrt(2)Average I^2 = I0^2 sin^2(omega t) over one full period (or equate the heat produced in R over a cycle to that of a steady current) and take the square root; write the same result for voltage.	Derivation	3	never		Never asked
53	AC through a pure resistor: current in phase with voltageApply V = V0 sin(omega t) to a resistor, obtain the current, state that current and voltage are in phase, and draw the phasor diagram and the two waveforms.	Derivation	2	never		Never asked
54	AC through a pure inductor: current lags by pi/2Apply Kirchhoff's law to an inductor on V = V0 sin(omega t) (V = L dI/dt), integrate to get the current, identify the inductive reactance, state that the current lags the voltage by pi/2, and draw the phasor diagram.	Derivation	3	never		Never asked
55	AC through a pure capacitor: current leads by pi/2Apply V = V0 sin(omega t) to a capacitor (q = C V), differentiate to get the current, identify the capacitive reactance, state that the current leads the voltage by pi/2, and draw the phasor diagram.	Derivation	3	never		Never asked
56	Phasor diagrams and waveforms for pure R, L and CSay what a phasor is, then for each of the three pure circuits draw the voltage and current phasors with the phase angle marked and the matching V-t and I-t curves on one pair of axes.	Diagram	2	never		Never asked
57	Reactance and impedance: definitions, formulas, unitDefine inductive reactance, capacitive reactance and impedance, give their formulas and SI unit (ohm), and state how each reactance changes with frequency, including the dc limit (X_L = 0, X_C infinite).	Statement	1	never		Never asked
58	Series LCR by phasors: impedance, phase angle, currentDraw the phasor diagram for a series LCR circuit (same current; V_R in phase with I, V_L leading by pi/2, V_C lagging by pi/2), combine V_L and V_C, add to V_R by Pythagoras, and obtain the impedance, the phase angle and the expression for the current.	Derivation	3	never		Never asked
59	LCR phasor diagram and impedance triangle: three casesDraw the voltage phasor diagram and the impedance triangle for X_L > X_C (voltage leads current, inductive), X_L < X_C (current leads, capacitive) and X_L = X_C (in phase, resistive), marking phi in each.	Diagram	2	never		Never asked
60	Series LR circuit: impedance and phase angle by phasorsDraw the phasor diagram for R and L in series, obtain the impedance and the angle by which the current lags the voltage, and write the current equation.	Derivation	2	never		Never asked
61	Series RC circuit: impedance and phase angle by phasorsDraw the phasor diagram for R and C in series, obtain the impedance and the angle by which the current leads the voltage, and write the current equation.	Derivation	2	never		Never asked
62	Graph of current versus frequency (resonance curve)Draw a labelled graph of rms current against frequency for a series LCR circuit, peaking at f0 with I_max = V/R, and show on the same axes how the peak becomes lower and broader for a larger R.	Graph	2	never		Never asked
63	Derive average power in an ac circuitMultiply V = V0 sin(omega t) by I = I0 sin(omega t - phi), average over one full cycle, and obtain the average power in terms of peak and rms values and the power factor; show it equals I_rms^2 R.	Derivation	3	never		Never asked
64	Wattless current: meaning and why average power is zeroExplain that in a purely inductive or purely capacitive circuit (and an LC circuit without resistance) the current is pi/2 out of phase with the voltage, so cos phi = 0 and the average power over a cycle is zero although a current flows; define wattless current.	Give reason	2	never		Never asked
65	Choke coil: why it limits ac without wasting powerExplain that a choke is a coil of large inductance and small resistance placed in series: its reactance omega L reduces the current, but its power factor is nearly zero so almost no energy is lost, unlike a series resistor which wastes I^2 R as heat; say why it is useless on dc.	Give reason	2	never		Never asked
66	Q factor and bandwidth: meaning and formulaSay what the quality factor of a series resonant circuit measures (sharpness of resonance; voltage magnification V_L/V at resonance), what bandwidth is (the range of frequency between the two half-power points), write the formulas, and state how R affects sharpness.	Statement	2	never		Never asked
67	Numericals: Q factor and bandwidthCalculate the Q factor of a series LCR circuit from R, L and C, and the bandwidth from the resonant frequency and Q.	Numericals	2	never		Never asked
68	LC oscillations: qualitative description of energy exchangeDescribe, with a four-stage sketch, how a charged capacitor joined to an inductor discharges and recharges with opposite polarity, so that energy passes back and forth between the electric field of C and the magnetic field of L; state the natural frequency and say why real oscillations die away (resistance).	Statement	2	never		Never asked
69	AC generator: labelled diagram, principle, construction, working, useDraw a labelled simple ac generator (field magnet N-S, armature coil, two slip rings, two brushes, external load), state the principle (electromagnetic induction: emf induced in a coil rotated in a magnetic field), describe the parts and explain how the output reverses every half turn; give its use.	Device	3	never		Never asked
70	AC generator theory: derive e = NBA omega sin(omega t)For a coil of N turns and area A rotating at angular speed omega in a uniform field B, write the flux at time t, differentiate to get the induced emf, identify the peak emf, and sketch the emf against time for one rotation marking the coil positions for zero and peak emf.	Derivation	3	never		Never asked
71	Numericals: peak and instantaneous emf of a generatorCalculate the peak emf of a rotating coil from N, B, A and the speed of rotation (convert rev/min to rad/s), then the instantaneous emf at a given time or angle, the rms emf and the peak current in a given load.	Numericals	2	never		Never asked
72	Voltage and current versus time for ac and dcSketch on labelled axes the variation with time of a steady dc (horizontal line) and of a sinusoidal ac (sine curve with peak value and period marked), for both voltage and current.	Graph	1	never		Never asked
73	Obtain self-inductance of a long solenoidStarting from B = mu0 n I inside a long solenoid, write the flux through each turn, the total flux linkage N phi, and divide by I to get L; add the form for a core of relative permeability mu_r and state what L depends on.	Derivation	2	never		Not in syllabus
74	Obtain mutual inductance of two coaxial solenoidsFor a long primary solenoid (N1 turns, length l) with a secondary of N2 turns wound over it, write B due to the primary current, the flux linked with the secondary, and divide by I1 to get M.	Derivation	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

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