The afternoon paper of 28 January 2026, the last 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 | 28 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 | Prism whose minimum deviation equals its own angle — range of the index | Ray Optics |
| 27 | Photons per second from a 6 mW laser at 663 nm | Dual Nature of Radiation and Matter |
| 28 | Magnetic field vector of a wave whose electric field is given | Electromagnetic Waves |
| 29 | Two masses joined by a stretched spring and released — angular frequency | Oscillations |
| 30 | Match viscosity, surface tension, pressure and surface energy to their dimensions | Units and Measurements |
| 31 | Five claims about electrostatic field lines and Gauss’s law — which hold | Electric Charges and Fields |
| 32 | Four readings in millimetres — the least count of the instrument used | Units and Measurements |
| 33 | Two nuclei, one with eight times the mass number — ratio of their radii | Nuclei |
| 34 | Percentage error in a spring constant from a mass and a timing measurement | Units and Measurements |
| 35 | Block sliding down an incline that is itself accelerating — the time taken | Laws of Motion |
| 36 | Four claims about capacitors and dielectrics — which hold | Electrostatic Potential and Capacitance |
| 37 | Wheatstone bridge with one arm heated — the potential difference that appears | Current Electricity |
| 38 | Which of four electrical quantities is not a measurable quantity at all | Current Electricity |
| 39 | Density and Young’s modulus both raised slightly — the new wave speed | Waves |
| 40 | Two diodes wired to two inputs — which gate the circuit makes | Semiconductor Electronics |
| 41 | Biconvex lens built from two plano-convex lenses — the magnification | Ray Optics |
| 42 | Where the field of a thick current-carrying cylinder is least | Moving Charges and Magnetism |
| 43 | Which vector does not change sign when the position vector is reversed | Rotational Motion |
| 44 | Five claims about a particle with x = 4t³ − 3t — which hold | Motion in a Straight Line |
| 45 | Mean free path of a molecule at a given temperature and pressure | Kinetic Theory of Gases |
| 46 | numeric Total work done by a system round a triangular cycle | Thermodynamics |
| 47 | numeric Two wavelengths in a double slit — where their bright fringes first coincide | Wave Optics |
| 48 | numeric Beats before and after loading a fork with wax — its original frequency | Waves |
| 49 | numeric Flywheel and hanging mass — kinetic energy of the wheel after a 3 m drop | Rotational Motion |
| 50 | numeric Inductor storing 16 J and wasting 32 W — ratio of reactance to resistance | Alternating Current |
Chapter by chapter
| Chapter | Questions | Marks |
|---|---|---|
| Units and Measurements | 3 | 12 |
| Current Electricity | 2 | 8 |
| Ray Optics | 2 | 8 |
| Rotational Motion | 2 | 8 |
| Waves | 2 | 8 |
| Alternating Current | 1 | 4 |
| Dual Nature of Radiation and Matter | 1 | 4 |
| Electric Charges and Fields | 1 | 4 |
| Electromagnetic Waves | 1 | 4 |
| Electrostatic Potential and Capacitance | 1 | 4 |
| Kinetic Theory of Gases | 1 | 4 |
| Laws of Motion | 1 | 4 |
| Motion in a Straight Line | 1 | 4 |
| Moving Charges and Magnetism | 1 | 4 |
| Nuclei | 1 | 4 |
| Oscillations | 1 | 4 |
| Semiconductor Electronics | 1 | 4 |
| Thermodynamics | 1 | 4 |
| Wave Optics | 1 | 4 |
All 19 shifts of JEE Main 2026, counted together chapter by chapter: JEE Main Physics important chapters.
Twenty chapters, with five of them taking two questions each. Three of the twenty-five questions were of the “which of these statements are correct” kind — on field lines, on capacitors, and on a particle’s motion — which is more of that format than any other shift in January.
Where the 100 marks sat
| Part of Physics | Questions | Marks | Share |
|---|---|---|---|
| Electrodynamics | 7 | 28 | 28% |
| Optics and Waves | 6 | 24 | 24% |
| Mechanics | 4 | 16 | 16% |
| Units, Dimensions and Measurement | 3 | 12 | 12% |
| Modern Physics and Electronics | 3 | 12 | 12% |
| Properties of Matter and Heat | 2 | 8 | 8% |
The odd one out of the whole year. Units and measurement got 12 marks here, three times what it got on 24 January morning, and optics and waves climbed to 24. Heat and properties of matter fell to 8, the lowest in any 2026 shift. A student who treats units as a throwaway chapter would have lost twelve marks in this one paper.
How tough it was
| Level | Questions | Share | Which ones |
|---|---|---|---|
| Straight recall or one step | 8 | 32% | 26, 30, 32, 33, 38, 39, 42, 43 |
| Two or three steps | 11 | 44% | 27, 28, 31, 36, 37, 40, 41, 44, 45, 48, 50 |
| Long or awkward | 6 | 24% | 29, 34, 35, 46, 47, 49 |
The block on an accelerating incline was the hardest question of Session 1: the answer has to be written with a double-angle identity before it matches any of the options, and getting the sign of the pseudo-force wrong gives one of the other three. The two-wavelength fringe coincidence is the other one worth practising — it needs the smallest whole numbers in the ratio 13 : 11 before any arithmetic can start.
All 25 Physics questions, solved
Q1 · Ray Optics · on the pattern of Q26
For a transparent prism the angle of minimum deviation turns out to be equal to the refracting angle of the prism itself. The refractive index n then satisfies ______.
Answer 1 < n < 2
Where it goes wrong Forgetting that n must exceed 1, and answering 0 < n < 2. Half the algebraic range is ruled out by physics.
Q2 · Dual Nature of Matter · on the pattern of Q27
A 6 mW laser works at 663 nm. The number of photons it emits per second is ______. (h = 6.63 × 10−34 J·s, c = 3 × 108 m/s.)
Answer 2 × 1016 per second
Where it goes wrong Leaving the power in milliwatts. 6 mW is 6 × 10−3 W, and the factor of a thousand changes the exponent.
Q3 · Electromagnetic Waves · on the pattern of Q28
A plane electromagnetic wave travels through free space with its electric field E = 54 sin(kz − ωt)ĵ V/m. The magnetic field vector of the wave is ______.
Answer B = −1.8 × 10−7 sin(kz − ωt)ĥ T
Where it goes wrong Getting the sign of the unit vector wrong by guessing. Work the cross product out: ĥ × ĵ = k̂ is the only one worth memorising, and the rest follow by cycling.
Q4 · Oscillations · on the pattern of Q29
A spring of force constant 150 N/m is held stretched between masses of 1 kg and 0.2 kg on a frictionless horizontal surface, and then released. The angular frequency of the resulting oscillation is ______ rad/s.
Answer 30 rad/s
Where it goes wrong Using the total mass 1.2 kg, or just one of the two. The reduced mass is always smaller than either, which is why the frequency comes out higher than you might expect.
Q5 · Units and Dimensions · on the pattern of Q30
Match each quantity to its dimensions: A. coefficient of viscosity, B. surface tension, C. pressure, D. surface energy. The options are ML−1T−2, ML2T−2, ML0T−2 and ML−1T−1.
Answer A → ML−1T−1, B → ML0T−2, C → ML−1T−2, D → ML2T−2
Where it goes wrong Giving surface energy the same dimensions as surface tension. They agree only when the energy is taken per unit area.
Q6 · Electric Charges and Fields · on the pattern of Q31
Which of these are correct? A. Electrostatic field lines form closed loops. B. The field lines point radially outward from a positive charge. C. Gauss’s law in this form holds only because the force is an inverse square one. D. The work done in taking a charge round a closed path in a static field is zero. E. Motion of a particle under the Coulomb force of a fixed charge must stay in a plane.
Answer B, C, D and E
Where it goes wrong Accepting A because magnetic field lines do form closed loops. The two fields differ in exactly this respect.
Q7 · Units and Measurement · on the pattern of Q32
A set of readings taken with one instrument comes out as 1.24 mm, 1.25 mm, 1.23 mm and 1.21 mm. The least count of that instrument is ______ mm.
Answer 0.01 mm
Where it goes wrong Working out the spread of the readings, 0.04 mm, and offering that. The spread measures the scatter in the measurement, not the resolution of the scale.
Q8 · Nuclei · on the pattern of Q33
One nucleus has mass number α and radius Rα; another has mass number β and radius Rβ, with β = 8α. The ratio Rα/Rβ is ______.
Answer 0.5
Where it goes wrong Answering 1/8. The mass number is in the volume, so the radius only changes by its cube root.
Q9 · Units and Measurement · on the pattern of Q34
A spring oscillator has T = 2π√(m/k). The mass is measured as 10 g with an accuracy of 10 mg, and the time for 50 oscillations is found to be 60 s on a watch whose resolution is 1 s. The percentage error in the spring constant k is ______ %.
Answer 3.43%
Where it goes wrong Dividing 1 s by T = 1.2 s instead of by the 60 s that was actually measured. Timing many oscillations at once is exactly how that error is cut down, and the calculation has to reflect it.
Q10 · Laws of Motion · on the pattern of Q35
A small block slides from the top of a frictionless inclined surface of angle θ and base length L, while the incline itself accelerates towards the left with a constant a0. The time the block takes to reach the lowest point is ______.
Answer √{ 4L / [g sin2θ − a0(1 + cos2θ)] }
Where it goes wrong Getting the pseudo-force the wrong way round, which flips the minus to a plus and matches one of the wrong options exactly. And then not converting to double angles, so the right answer looks like none of the choices.
Q11 · Capacitance · on the pattern of Q36
Which of these are correct? A. The effective capacitance of capacitors in series is always smaller than the smallest one in the set. B. When a dielectric is placed between charged plates, no displacement of charge can occur because a dielectric is an insulator. C. Increasing the plate area, or reducing the thickness of the dielectric, both raise the capacitance. D. For a point charge, concentric spheres centred on it are equipotential surfaces.
Answer A, C and D
Where it goes wrong Accepting B because “insulator” sounds like “nothing moves”. Charge does not flow through a dielectric, but it does shift within each molecule.
Q12 · Current Electricity · on the pattern of Q37
A Wheatstone bridge has all four arms equal at 100 Ω and is fed from a 21 V supply, so it is balanced. One arm is then heated and its resistance rises by 10%. The potential difference that now appears across the galvanometer arm is ______ V.
Answer 0.5 V
Where it goes wrong Expecting 10% of the supply. The imbalance is diluted by the whole divider, so it comes out far smaller.
Q13 · Current Electricity · on the pattern of Q38
Which of these is not a measurable quantity: resistance, displacement current, voltage, or voltage difference?
Answer voltage
Where it goes wrong Picking displacement current because it sounds abstract. It is a real, measurable quantity; it is the bare word “voltage” that is not well defined.
Q14 · Waves · on the pattern of Q39
A longitudinal wave travels at 400 m/s in a metal bar. If the density of the material is raised by 0.5% and its Young’s modulus by 1%, the speed becomes about ______ m/s.
Answer about 401 m/s
Where it goes wrong Adding the two percentages, or forgetting the factor of a half that the square root brings. The denominator also changes sign on the way out.
Q15 · Semiconductor Electronics · on the pattern of Q40
Two p-n junction diodes have their anodes connected to inputs A and B, and their cathodes joined together at the output C, which returns to ground through a resistor. The circuit works as a ______ gate.
Answer OR gate
Where it goes wrong Calling it an AND gate because both diodes are in the circuit. Follow one case at a time: a single high input is enough to drive the output high.
Q16 · Ray Optics · on the pattern of Q41
A biconvex lens is made by sticking together, at their flat faces, two thin plano-convex lenses of refractive index 1.5 whose curved faces have radii 10 cm and 15 cm. An object is placed 36 cm to the left of the pair. The magnification of the image is ______.
Answer −0.5 (half the size, inverted, real)
Where it goes wrong Using the lens maker’s formula once with both radii and n = 1.5, which happens to give the same answer here only because both halves share the same index. Doing the two lenses separately and adding the powers always works, even when the two glasses differ.
Q17 · Moving Charges and Magnetism · on the pattern of Q42
A long cylindrical conductor of large cross-section carries a current spread evenly over that cross-section. Which statement about its magnetic field is correct: maximum at the axis, minimum at the surface, minimum at the axis, or the same everywhere in the cross-section?
Answer minimum at the axis
Where it goes wrong Assuming the field is strongest where the current is “most concentrated”, at the centre. On the axis there is no enclosed current at all, so there is no field.
Q18 · Rotational Motion · on the pattern of Q43
When the position vector r is replaced by −r, which of these does not change sign: velocity, acceleration, linear momentum, or angular momentum?
Answer angular momentum
Where it goes wrong Reasoning that L contains r, so it must flip. It contains r once and p once, and the pair of sign changes undo each other.
Q19 · Motion in a Straight Line · on the pattern of Q44
A particle starts at t = 0 with x(t) = 4t³ − 3t. Which of these are correct? A. It returns to the origin 0.866 units of time later. B. It is 1 unit from the origin at its turning point. C. Its acceleration is never negative. D. It is 0.5 units from the origin at its turning point. E. It never turns back, because the acceleration is never negative.
Answer A, B and C
Where it goes wrong Accepting E because C is true. A body can turn round while its acceleration stays one way; it only needs the velocity to pass through zero.
Q20 · Kinetic Theory of Gases · on the pattern of Q45
The mean free path of a molecule of diameter 5 × 10−10 m at 41 °C and a pressure of 1.38 × 105 Pa is ______ m. (kB = 1.38 × 10−23 J/K.)
Answer 2√2 × 10−8 m, about 2.8 × 10−8 m
Where it goes wrong Leaving out the √2, which comes from the fact that the other molecules are moving too, not standing still.
Q21 · Thermodynamics · numeric · on the pattern of Q46
A system is taken round the triangular cycle ABC on a p-V diagram, with A at (1 m³, 10 Pa), B at (3 m³, 10 Pa) and C at (1 m³, 30 Pa), returning from C to A. The total work done by the system is ______ J.
Answer −20 J (that is, 20 J is done on the system)
Where it goes wrong Giving +20 J, the bare area. The direction round the loop fixes the sign: clockwise means work out, anticlockwise means work in.
Q22 · Wave Optics · numeric · on the pattern of Q47
A beam containing wavelengths 650 nm and 550 nm lights up a double slit of separation 2 mm, with the screen 1.2 m away. The least distance from the central maximum at which bright fringes of both wavelengths fall together is ______ × 10−5 m.
Answer 429 × 10−5 m, that is 4.29 mm
Where it goes wrong Pairing the larger order with the larger wavelength. It is the other way about: the longer wavelength needs fewer fringes to reach the same place.
Q23 · Waves · numeric · on the pattern of Q48
Two tuning forks A and B sounded together give 8 beats in 2 s. When A is loaded with wax the beats fall to 4 in 2 s. If B has a frequency of 380 Hz, the original frequency of A was ______ Hz.
Answer 384 Hz
Where it goes wrong Stopping at “384 or 376”. The wax is there precisely to settle which, and the rule is that it always lowers the frequency.
Q24 · Rotational Motion · numeric · on the pattern of Q49
A flywheel of mass 3 kg and radius 5 m, free to turn about a horizontal axis, has a light string wound round it with a 3 kg mass tied to the loose end. The mass is released from rest. The kinetic energy of the wheel when the mass has descended 3 m is ______ J. (g = 10 m/s2; treat the flywheel as a uniform disc.)
Answer 30 J
Where it goes wrong Giving the whole 90 J to the wheel. The hanging mass is moving too, and here it takes twice as much of the energy as the wheel does.
Q25 · Alternating Current · numeric · on the pattern of Q50
An inductor stores 16 J of magnetic energy and wastes 32 W as heat in its own resistance when an alternating current of 2 A r.m.s. at 50 Hz flows through it. The ratio of its inductive reactance to its resistance is ______. (π = 3.14.)
Answer 314
Where it goes wrong Using the peak current for the stored energy. The 2 A is already an r.m.s. value, and ½LIrms2 is the average energy, which is what “stores 16 J” means here.
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, 28 January 2026, is on its own page, and the other January dates are 21, 22, 23 and 24 January.
All shifts, date by date: JEE Main Previous Years Papers.
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