The afternoon paper of 22 January 2026, the fourth shift of Session 1. Below is the Physics section question by question, the chapter split, where the hundred marks sat, how tough it was, and the official answer key from NTA.
The shift
| Date | 22 January 2026 |
|---|---|
| Shift | Shift 2 — 3:00 PM to 6:00 PM IST |
| Paper | Paper 1 (B.E./B.Tech) |
| Whole paper | 75 questions, 300 marks, 180 minutes |
| Physics | Q26 to Q50 — Section A 20 MCQ (80 marks), Section B 5 numeric (20 marks) |
| Marking | +4 right, −1 wrong, nothing for a blank |
Physics, question by question
| Q | What it asked | Chapter |
|---|---|---|
| 26 | Pendulum experiment for g — which plot of length against time period is right | Units and Measurements |
| 27 | Ammeter reading at the instant a switch is closed on a coil circuit | Electromagnetic Induction |
| 28 | Power line of 2 Ω delivering 1 kW at 250 V — percentage efficiency | Current Electricity |
| 29 | Photoelectrons with zero kinetic energy — angular frequency of the light | Dual Nature of Radiation and Matter |
| 30 | Two statements on the period of a satellite skimming the Earth | Gravitation |
| 31 | Five equal charges at the corners of a pentagon — potential and field at the centre | Electrostatic Potential and Capacitance |
| 32 | Capillary rise when radius, density and surface tension each fall by 1% | Mechanical Properties of Fluids |
| 33 | Gap between the longest Paschen and the longest Balmer wavelength | Atoms |
| 34 | Two statements on splitting the kinetic energy of a many-particle system | Centre of Mass |
| 35 | Unit of permittivity multiplied into a changing electric field | Units and Measurements |
| 36 | Open organ pipe — length from the gap between the third and sixth harmonics | Waves |
| 37 | Where the object must sit in the parallax method for a concave mirror | Ray Optics |
| 38 | Two statements on the work done by a conservative force | Work, Energy and Power |
| 39 | Amplitude of the magnetic field in a laser beam of known intensity | Electromagnetic Waves |
| 40 | Collision frequency in a gas of smaller, heavier molecules at the same T, P and density | Kinetic Theory of Gases |
| 41 | Two point masses striking the ends of a bar and sticking — ratio of v to ω | Rotational Motion |
| 42 | Three charged bubbles merging into one — ratio of the potentials | Electrostatic Potential and Capacitance |
| 43 | Wavelength of the same light on passing from water into a denser medium | Ray Optics |
| 44 | Which statements about the central maximum in single slit diffraction hold | Wave Optics |
| 45 | Correct truth table for a given gate combination | Semiconductor Electronics |
| 46 | numeric Loop spun about its diameter in a field — radius from the emf at 30° | Electromagnetic Induction |
| 47 | numeric Two masses over a heavy disc pulley — speed after falling 3.6 m | Rotational Motion |
| 48 | numeric Gas squeezed from 60 cm³ to 20 cm³ as it warms — final pressure | Thermodynamics |
| 49 | numeric Charged capacitor joined to an uncharged one — charge that ends up on it | Electrostatic Potential and Capacitance |
| 50 | numeric Mobility of electrons in a wire from the current and the voltage | Current Electricity |
Chapter by chapter
| Chapter | Questions | Marks |
|---|---|---|
| Electrostatic Potential and Capacitance | 3 | 12 |
| Current Electricity | 2 | 8 |
| Electromagnetic Induction | 2 | 8 |
| Ray Optics | 2 | 8 |
| Rotational Motion | 2 | 8 |
| Units and Measurements | 2 | 8 |
| Atoms | 1 | 4 |
| Centre of Mass | 1 | 4 |
| Dual Nature of Radiation and Matter | 1 | 4 |
| Electromagnetic Waves | 1 | 4 |
| Gravitation | 1 | 4 |
| Kinetic Theory of Gases | 1 | 4 |
| Mechanical Properties of Fluids | 1 | 4 |
| Semiconductor Electronics | 1 | 4 |
| Thermodynamics | 1 | 4 |
| Wave Optics | 1 | 4 |
| Waves | 1 | 4 |
| Work, Energy and Power | 1 | 4 |
All 19 shifts of JEE Main 2026, counted together chapter by chapter: JEE Main Physics important chapters.
Twenty chapters in twenty-five questions, the widest spread of any January shift. Five chapters took two questions each and fifteen took exactly one. A student who had left even three chapters untouched would have met a gap here.
Where the 100 marks sat
| Part of Physics | Questions | Marks | Share |
|---|---|---|---|
| Electrodynamics | 8 | 32 | 32% |
| Mechanics | 5 | 20 | 20% |
| Optics and Waves | 4 | 16 | 16% |
| Properties of Matter and Heat | 3 | 12 | 12% |
| Modern Physics and Electronics | 3 | 12 | 12% |
| Units, Dimensions and Measurement | 2 | 8 | 8% |
Electrodynamics at 32 marks again, the same as the 21 January afternoon shift. Heat and properties of matter came down to 12, the lightest it was treated in January.
How tough it was
| Level | Questions | Share | Which ones |
|---|---|---|---|
| Straight recall or one step | 8 | 32% | 28, 31, 32, 36, 43, 48, 49, 50 |
| Two or three steps | 12 | 48% | 26, 29, 30, 34, 35, 37, 38, 39, 42, 44, 46, 47 |
| Long or awkward | 5 | 20% | 27, 33, 40, 41, 45 |
The friendliest January shift on the numbers: eight questions were one line each, and the five numeric questions in Section B were all straightforward. The two Bohr-series wavelengths and the bar struck at both ends were the only real time sinks.
All 25 Physics questions, solved
Q1 · Units and Measurement · on the pattern of Q26
In a simple pendulum experiment, g is found by measuring the time period T for several lengths L. Which graph comes out as a straight line through the origin?
Answer L plotted against T2
Where it goes wrong Plotting T against L and trying to read a slope off a curve. Square the period first; that is the whole point of the graph.
Q2 · Electromagnetic Induction · on the pattern of Q27
A 9 Ω resistor and a 4 mH inductor are joined in series across an 18 V battery through a switch, with an ammeter in the circuit. The ammeter reading at the instant the switch is closed is ______ A.
Answer zero
Where it goes wrong Giving 2 A, the steady value. That is the reading long afterwards, not at the instant of switching.
Q3 · Current Electricity · on the pattern of Q28
A power line of total resistance 2 Ω delivers 1 kW of power at 250 V. The percentage efficiency of the line is ______.
Answer 96.9%
Where it goes wrong Dividing by 1000 instead of 1032. The delivered power is the output; the input is output plus loss.
Q4 · Dual Nature of Matter · on the pattern of Q29
Light falls on a metal plate whose work function is 110 × 10−20 J. The photoelectrons come out with zero kinetic energy. The angular frequency of the incident light is ______ rad/s. (h = 6.63 × 10−34 J·s.)
Answer 1.04 × 1016 rad/s
Where it goes wrong Giving the answer as ν and forgetting the 2π. The question asks for angular frequency, not frequency.
Q5 · Gravitation · on the pattern of Q30
Two statements about a satellite circling the Earth just above the surface. Statement I: its period depends on the density of the Earth. Statement II: its period is T = 2π√(Re/g). Which is true?
Answer Both statements are true
Where it goes wrong Calling Statement I false because the radius seems to matter. For a close orbit it cancels out, and only the density survives.
Q6 · Electrostatic Potential · on the pattern of Q31
Five equal positive charges q are placed at the five corners of a regular pentagon of circumradius r. The potential V and the field E at the centre O are ______.
Answer V = 5q/4πε0r and E = 0
Where it goes wrong Assuming an odd number of charges cannot cancel. Symmetry, not parity, is what matters — any regular polygon of equal charges gives zero field at the centre.
Q7 · Mechanical Properties of Fluids · on the pattern of Q32
A liquid rises to a height h in a vertical capillary tube. The inner radius of the tube, the density of the liquid and the surface tension of the liquid each decrease by 1%. The height changes by ______ %.
Answer +1%
Where it goes wrong Adding all three as −1% and answering −3%. Quantities in the denominator come in with the opposite sign.
Q8 · Atoms · on the pattern of Q33
The shortest wavelength of the Lyman series is 91 nm. The difference between the longest wavelength of the Paschen series and the longest wavelength of the Balmer series is about ______ nm.
Answer about 1216 nm
Where it goes wrong Taking the longest wavelength of a series as the limit. The limit is the shortest; the longest comes from the smallest energy gap in the series.
Q9 · Centre of Mass · on the pattern of Q34
Two statements about a system of many particles. Statement I: the total kinetic energy is the sum of the kinetic energies of all the particles. Statement II: the total kinetic energy can also be written as the kinetic energy of the centre of mass plus the kinetic energy of the particles measured relative to the centre of mass. Which is true?
Answer Both statements are true
Where it goes wrong Calling Statement II false because it looks like double counting. It is the same energy written two ways, and the cross terms vanish exactly.
Q10 · Units and Dimensions · on the pattern of Q35
If ε0 is the permittivity of free space and E is an electric field, the SI unit of ε0 multiplied by the rate of change of E with time is ______.
Answer A/m2
Where it goes wrong Multiplying by time instead of dividing. ε0Et would be C·s/m2, which is not a current density at all.
Q11 · Waves · on the pattern of Q36
In an open organ pipe the third and sixth harmonic frequencies differ by 2200 Hz. The length of the pipe is ______ mm. (Speed of sound in air = 330 m/s.)
Answer 225 mm
Where it goes wrong Using the closed-pipe formula with only odd harmonics. The pipe here is open at both ends, so every integer multiple is present.
Q12 · Ray Optics · on the pattern of Q37
In the parallax method for finding the focal length of a concave mirror, where must the object be placed?
Answer Anywhere beyond the focus F of the mirror
Where it goes wrong Insisting on the object being beyond C. That gives a real image too, but it is not the only position that does.
Q13 · Work, Energy and Power · on the pattern of Q38
Two statements. Statement I: for an object moving from r1 to r2 in a conservative force field F, the work done by the force is W = −∫F·dr. Statement II: since an object can take infinitely many paths between two points, the work done by a conservative force depends on the path. Which is true?
Answer Both statements are false
Where it goes wrong Letting the familiar minus sign pass unchecked. It is correct for ΔU and wrong for W, and the two are easy to swap.
Q14 · Electromagnetic Waves · on the pattern of Q39
A laser beam has an intensity of 4.0 × 1014 W/m2. The amplitude of the magnetic field in the beam is ______ T. (ε0 = 8.85 × 10−12 C2/N·m2, c = 3 × 108 m/s.)
Answer about 1.83 T
Where it goes wrong Working out E0 first and then dividing by c, which is fine but invites a slip. Going straight through the magnetic form is one step.
Q15 · Kinetic Theory of Gases · on the pattern of Q40
Two boxes hold ideal gases A and B at the same temperature, the same pressure and the same number density. A molecule of A is half the size of one of B, and four times as heavy. If the collision frequency in B is 32 × 1018 per second, the collision frequency in A is ______ per second.
Answer 4 × 1018 per second
Where it goes wrong Changing the number density because the molecules are smaller. The question fixes the number density, so only size and mass matter.
Q16 · Rotational Motion · on the pattern of Q41
A uniform bar of length 12 cm and mass 20m lies on a smooth horizontal table. Two point masses, each of mass m, move in opposite directions with the same speed v in the plane of the table, at right angles to the bar. They strike the two ends of the bar at the same instant and stick to it. The whole system then turns with angular velocity ω. The ratio v/ω is ______.
Answer 0.26 m
Where it goes wrong Treating the two angular momenta as cancelling. Opposite velocities arriving at opposite ends spin the bar the same way, so they add.
Q17 · Electrostatic Potential · on the pattern of Q42
Three identical water bubbles, each carrying the same charge, merge into one bigger bubble. The ratio of the potential on one of the original bubbles to the potential on the bigger one is ______.
Answer 1 : 32/3
Where it goes wrong Adding the radii instead of the volumes. The radius grows only as the cube root of the number merged.
Q18 · Ray Optics · on the pattern of Q43
Light passing through water has a wavelength of 540 nm. The refractive index of water is 4/3. The wavelength of the same light while passing through a transparent medium of refractive index 3/2 is ______ nm.
Answer 480 nm
Where it goes wrong Scaling 540 nm by 4/3 ÷ 3/2 in one go without care over which way round it goes. Find the vacuum wavelength first; it is the fixed reference.
Q19 · Wave Optics · on the pattern of Q44
For single slit diffraction, which of these are true? A. The width of the central maximum grows when the wavelength is increased at fixed slit width. B. It grows when the wavelength is decreased at fixed slit width. C. It grows when the slit is made narrower at fixed wavelength. D. It grows when the slit is made wider at fixed wavelength.
Answer A and C only
Where it goes wrong Carrying over the intuition from a double slit, where a smaller separation widens the fringes. The direction is the same here, but the quantity is the slit width itself, not a separation.
Q20 · Semiconductor Electronics · on the pattern of Q45
Inputs A and B are fed to an OR gate and also to an AND gate. The two outputs are then fed to a second AND gate, whose output is Y. Write the truth table for Y.
Answer Y = A AND B — Y is 1 only when A = B = 1
Where it goes wrong Writing out the table row by row without noticing the arrangement simplifies. Spotting that one input already implies the other saves all four rows.
Q21 · Electromagnetic Induction · numeric · on the pattern of Q46
A conducting circular loop is spun about its own diameter at a steady 100 rad/s in a magnetic field of 0.5 T at right angles to the axis of rotation. When the loop has turned 30° from the horizontal position, the induced emf is 15.4 mV. The radius of the loop is ______ mm. (π = 22/7.)
Answer 14 mm
Where it goes wrong Using cos30° because 30° sounds like an angle from the field. Here it is measured from the position where the emf is zero, so it is the sine that enters.
Q22 · Rotational Motion · numeric · on the pattern of Q47
Masses m and 2m are joined by a light string passing over a pulley which is a disc of mass 30m and radius 0.1 m, mounted in a vertical plane and free to turn about its axis. The 2m mass is released from rest. Its speed after it has fallen 3.6 m is ______ m/s. (The string does not slip; g = 10 m/s2.)
Answer 2 m/s
Where it goes wrong Adding the pulley’s full mass 30m to the bracket. It is I/r2 that goes in, which for a disc is half the mass.
Q23 · Thermodynamics · numeric · on the pattern of Q48
A cylinder of volume 60 cm3 holds a gas at 27 °C and 2 atmospheres. The gas is squeezed to a final volume of 20 cm3 while its temperature is allowed to rise to 77 °C. The final pressure is ______ atmospheres.
Answer 7 atmospheres
Where it goes wrong Putting 27 and 77 straight into the ratio. The gas equation needs absolute temperature, so add 273 to both.
Q24 · Capacitance · numeric · on the pattern of Q49
A capacitor P of 10 μF is charged fully to 6.0 V and disconnected from the battery. It is then connected across an uncharged capacitor Q of 20 μF. The charge that ends up on Q is α × 10−5 C. The value of α is ______.
Answer 4
Where it goes wrong Assuming the charge splits in half. It splits in proportion to the capacitances, because the voltage is what the two end up sharing.
Q25 · Current Electricity · numeric · on the pattern of Q50
A cylindrical conductor 2 m long with a cross-section of 0.2 mm2 carries 1.6 A when its ends are joined to a 2 V battery. The mobility of the electrons is α × 10−3 m2/V·s. The value of α is ______. (Electron concentration = 5 × 1028/m3, e = 1.6 × 10−19 C.)
Answer 1
Where it goes wrong Leaving the area in mm2. 0.2 mm2 is 0.2 × 10−6 m2, not 0.2 × 10−3.
The official answer key
NTA did not publish the Session 1 question papers. They were shown only inside each candidate’s own login during the answer key challenge window in February 2026, and that window is closed. The one official file for this shift is the final answer key, which covers all ten January shifts. Shift 1 of the same day, 22 January 2026, is on its own page, and the other January dates are 21, 23, 24 and 28 January.
All shifts, date by date: JEE Main Previous Years Papers.
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