The afternoon paper of 23 January 2026, the sixth 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 | 23 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 | Block sliding down an incline given a push up — distance before it stops | Laws of Motion |
| 27 | Same work done isothermally and then adiabatically — the final temperature | Thermodynamics |
| 28 | Two beads, one on a curved wire and one on a straight wire — which arrives first | Work, Energy and Power |
| 29 | Two short dipoles 80 cm apart — field at a point equidistant from both | Electric Charges and Fields |
| 30 | Paratrooper, 2 s of free fall then steady deceleration — height of the aeroplane | Motion in a Straight Line |
| 31 | Which pair of nuclei are isobars | Nuclei |
| 32 | Two balancing lengths on a potentiometer — percentage error in the emf ratio | Units and Measurements |
| 33 | Body at rest explodes into three fragments — speed of the heaviest | Centre of Mass |
| 34 | Mica sheet slipped into a connected capacitor — its dielectric constant | Electrostatic Potential and Capacitance |
| 35 | Reflected beam fully polarised — the angle of the refracted beam | Wave Optics |
| 36 | Speed of light in vacuum against that in a medium of given K and μ | Electromagnetic Waves |
| 37 | Metal sphere dropped in glycerine — terminal velocity | Mechanical Properties of Fluids |
| 38 | Prism with a coated back face — incidence needed for total internal reflection | Ray Optics |
| 39 | Correct truth table for the given gate circuit | Semiconductor Electronics |
| 40 | Air bubble rising from the bottom of a pool — its volume at the surface | Kinetic Theory of Gases |
| 41 | Circular loop reshaped into a square in half a second — the emf | Electromagnetic Induction |
| 42 | Two charges sitting in an external field — the electrostatic energy | Electrostatic Potential and Capacitance |
| 43 | Loop slid inside a solenoid carrying an alternating current — r.m.s. current | Electromagnetic Induction |
| 44 | Helium heated under a light piston — how far the piston travels | Thermodynamics |
| 45 | Current in a triangular loop — field at the centroid | Moving Charges and Magnetism |
| 46 | numeric Energy released when 47 g of uranium-235 fissions completely | Nuclei |
| 47 | numeric Powers in a formula for the time to reach terminal velocity | Units and Measurements |
| 48 | numeric Disc with a piece cut out — moment of inertia of what is left | Rotational Motion |
| 49 | numeric Two object positions giving images of the same size — the focal length | Ray Optics |
| 50 | numeric Temperature at which the speed of sound in air doubles | Waves |
Chapter by chapter
| Chapter | Questions | Marks |
|---|---|---|
| Electromagnetic Induction | 2 | 8 |
| Electrostatic Potential and Capacitance | 2 | 8 |
| Nuclei | 2 | 8 |
| Ray Optics | 2 | 8 |
| Thermodynamics | 2 | 8 |
| Units and Measurements | 2 | 8 |
| Centre of Mass | 1 | 4 |
| Electric Charges and Fields | 1 | 4 |
| Electromagnetic Waves | 1 | 4 |
| Kinetic Theory of Gases | 1 | 4 |
| Laws of Motion | 1 | 4 |
| Mechanical Properties of Fluids | 1 | 4 |
| Motion in a Straight Line | 1 | 4 |
| Moving Charges and Magnetism | 1 | 4 |
| Rotational Motion | 1 | 4 |
| Semiconductor Electronics | 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-one chapters in twenty-five questions — the thinnest spread of the whole year. Only four chapters got a second question, and seventeen appeared exactly once. Mechanics was split across five different chapters rather than concentrated in two.
Where the 100 marks sat
| Part of Physics | Questions | Marks | Share |
|---|---|---|---|
| Electrodynamics | 7 | 28 | 28% |
| Mechanics | 5 | 20 | 20% |
| Properties of Matter and Heat | 4 | 16 | 16% |
| Optics and Waves | 4 | 16 | 16% |
| Modern Physics and Electronics | 3 | 12 | 12% |
| Units, Dimensions and Measurement | 2 | 8 | 8% |
The most even split of any January shift, and almost exactly the 2026 average. Nothing was over-weighted and nothing was skipped.
How tough it was
| Level | Questions | Share | Which ones |
|---|---|---|---|
| Straight recall or one step | 7 | 28% | 31, 33, 35, 36, 41, 49, 50 |
| Two or three steps | 12 | 48% | 26, 27, 30, 32, 34, 37, 40, 44, 45, 46, 47, 48 |
| Long or awkward | 6 | 24% | 28, 29, 38, 39, 42, 43 |
The loop sliding inside an alternating-current solenoid was the single hardest question in January: it needed the flux, a derivative, a root-mean-square step and careful powers of ten. The two charges sitting in an external field was the second, because the external potential and the mutual energy both had to be counted and it is easy to drop one.
All 25 Physics questions, solved
Q1 · Laws of Motion · on the pattern of Q26
A block is sliding down an incline of slope θ at a steady speed. At t = 0 it is given a push up the slope so that it moves up with speed u. The distance it travels up the incline before its speed falls to zero is ______.
Answer u2 / 4g sinθ
Where it goes wrong Missing the clue in “sliding down at a steady speed”. That one phrase is what fixes μ = tanθ; without it the question cannot be answered at all.
Q2 · Thermodynamics · on the pattern of Q27
One mole of an ideal diatomic gas expands from V to 2V isothermally at 27 °C and does W joule of work. The same gas, again starting at 27 °C, now expands adiabatically and does the same amount of work W. Its final temperature is about ______ °C. (loge2 = 0.693.)
Answer about −56 °C
Where it goes wrong Using CP for the adiabatic step. No heat is exchanged, so all the work comes from the internal energy, and that is CV.
Q3 · Work, Energy and Power · on the pattern of Q28
A bead slides from rest down a smooth wire bent into some curve, from a point A to a point B which is 1.8 m lower. Its speed at B is ______ m/s. (g = 10 m/s2.)
Answer 6 m/s
Where it goes wrong Trying to work along the curve. The drop in height is the only thing that matters for the speed.
Q4 · Electric Charges and Fields · on the pattern of Q29
A short electric dipole is made of charges +2 μC and −2 μC separated by 1 cm. The electric field at a point on the axis of the dipole, 40 cm from its centre, is ______ N/C. (1/4πε0 = 9 × 109 SI units.)
Answer 5625 N/C, that is 5.625 × 103 N/C
Where it goes wrong Using kp/r3, the equatorial value, on the axis. The axial field is twice the equatorial one at the same distance.
Q5 · Motion in a Straight Line · on the pattern of Q30
A paratrooper jumps from an aeroplane, falls freely for 2 s, then opens the parachute and decelerates steadily at 3 m/s2. At a height of 10 m above the ground he is descending at 5 m/s. The height of the aeroplane was ______ m. (g = 10 m/s2.)
Answer 92.5 m
Where it goes wrong Forgetting the last 10 m. He is not on the ground when the 5 m/s is quoted, so that height has to be added back.
Q6 · Nuclei · on the pattern of Q31
Which of these pairs are isobars? (a) 236U and 238U, (b) 198Hg and 197Au, (c) 2H and 3H, (d) 3H and 3He.
Answer (d) 3H and 3He
Where it goes wrong Swapping isobars and isotopes. Isotopes share Z, the element; isobars share A, the mass number.
Q7 · Units and Measurement · on the pattern of Q32
Two cells are compared on a potentiometer and the balancing lengths come out as 200 cm and 100 cm. The least count of the scale is 1 cm. The percentage error in the ratio of the emfs is ______.
Answer 1.5%
Where it goes wrong Subtracting the second term because l2 is in the denominator. For the maximum error in a quotient the relative errors are always added.
Q8 · Centre of Mass · on the pattern of Q33
A body of mass 14 kg at rest explodes into three fragments whose masses are in the ratio 2 : 2 : 3. The two equal fragments fly off at right angles to each other, each at 18 m/s. The speed of the heaviest fragment is ______ m/s.
Answer 12√2 m/s, about 17 m/s
Where it goes wrong Adding the two momenta as 144 instead of 72√2. They are perpendicular, so the Pythagorean sum is what the third fragment has to balance.
Q9 · Capacitance · on the pattern of Q34
A parallel plate capacitor with a plate separation of 5 mm is charged by a battery. A mica sheet 2 mm thick is now slipped in, with the plates still joined to the battery, and the capacitor is found to draw 25% more charge. The dielectric constant of the mica is ______.
Answer 2
Where it goes wrong Using C = Kε0A/d, which is for a slab that fills the whole gap. Here 3 mm of the gap is still air.
Q10 · Wave Optics · on the pattern of Q35
Unpolarised light falls on a glass plate in air at the particular angle for which the reflected beam is completely linearly polarised. The refracted beam then makes an angle of about ______ with the normal. (Refractive index of glass = 1.52, tan−1(1.52) = 56.7°.)
Answer about 33.3°
Where it goes wrong Giving the Brewster angle itself. The question asks for the refracted ray, which is the complement of it.
Q11 · Electromagnetic Waves · on the pattern of Q36
The ratio of the speed of electromagnetic waves in vacuum to their speed in a medium of dielectric constant K = 3 and permeability μ = 2μ0 is ______.
Answer √6 : 1
Where it goes wrong Writing n = √K and ignoring the permeability. That shortcut is only valid when the medium is non-magnetic, μ = μ0, which it is not here.
Q12 · Mechanical Properties of Fluids · on the pattern of Q37
A small metal sphere of diameter 2 mm and density 10.5 g/cm3 is dropped into glycerine of viscosity 10 poise and density 1.5 g/cm3. Its terminal velocity is ______ cm/s. (g = 10 m/s2.)
Answer 2 cm/s
Where it goes wrong Leaving the viscosity in poise. One poise is 0.1 Pa·s, so 10 poise is exactly 1 in SI — convenient here, but it still has to be checked.
Q13 · Ray Optics · on the pattern of Q38
A prism of angle 75° is made of material of refractive index √3, and its back face is coated with a thin film of refractive index 1.5. For total internal reflection to happen at that back face, the angle of incidence at the front face must be less than about ______.
Answer about 27°
Where it goes wrong Using 1/√3 for sin C, as though the film were air. The rarer medium at that face is the film, so its index goes on top.
Q14 · Semiconductor Electronics · on the pattern of Q39
Inputs A and B are fed to a NOR gate, and the output of the NOR gate is fed to a NOT gate, giving Y. Write the truth table for Y.
Answer Y = A OR B — Y is 0 only when A = B = 0
Where it goes wrong Assuming two negations somewhere in a circuit always cancel. They do here because they sit one straight after the other; a NOT on each input instead would give something quite different.
Q15 · Kinetic Theory of Gases · on the pattern of Q40
An air bubble of volume 2.9 cm3 rises from the bottom of a swimming pool 5 m deep, where the water is at 17 °C, to the surface, where it is at 27 °C. The volume of the bubble at the surface is ______ cm3. (g = 10 m/s2, density of water = 103 kg/m3, atmospheric pressure = 105 Pa.)
Answer 4.5 cm3
Where it goes wrong Using only the water pressure at the bottom and leaving out the atmosphere above it. Both press on the bubble.
Q16 · Electromagnetic Induction · on the pattern of Q41
A circular loop of radius 7 cm lies in a uniform field of 0.2 T at right angles to its plane. The loop is reshaped into a square in 0.5 s. The emf induced is ______ mV. (π = 22/7.)
Answer 1.32 mV
Where it goes wrong Taking the square’s side as the diameter or the radius. The wire’s length is what is conserved, so the circumference becomes the perimeter.
Q17 · Electrostatic Potential · on the pattern of Q42
Charges of 7 μC and −2 μC are placed at (−9, 0, 0) cm and (9, 0, 0) cm in an external field E = (A/r2)r̂, where A = 9 × 105 N·C−1m2. Taking the potential at infinity to be zero, the electrostatic energy of the arrangement is ______ J.
Answer 49.3 J
Where it goes wrong Counting only the mutual energy, or only the energy in the external field. Both belong in the total, and here the external part is by far the bigger of the two.
Q18 · Electromagnetic Induction · on the pattern of Q43
A long solenoid of 500 turns per metre carries I = 10 sin(ωt) A with ω = 1000 rad/s. A circular loop of radius 1 cm and resistance 10 Ω lies coaxially well inside it. The r.m.s. current in the loop is α/√2 microampere. The value of α is about ______.
Answer about 197
Where it goes wrong Using the solenoid’s own radius for the flux area. The flux that matters is the flux through the small loop, so it is the loop’s area that goes in.
Q19 · Thermodynamics · on the pattern of Q44
One mole of helium is held in a cylinder of cross-section 20 cm2 under a light, frictionless, movable piston, with atmospheric pressure 105 Pa outside. The gas is heated slowly with 100 J of heat. The piston moves out by ______ cm.
Answer 20 cm
Where it goes wrong Putting all 100 J into the work. At constant pressure only two fifths of the heat becomes work for a monatomic gas; the rest warms the gas.
Q20 · Moving Charges and Magnetism · on the pattern of Q45
A current of 2 A flows round a loop in the shape of an equilateral triangle of side 4√3 cm. The magnetic field at its centroid is α × 10−5 T. The value of α is ______. (μ0 = 4π × 10−7 SI units.)
Answer 3√3, about 5.2
Where it goes wrong Using the infinite-wire formula μ0I/2πd. Each side is short, so the sines of the two end angles have to be put in.
Q21 · Nuclei · numeric · on the pattern of Q46
The average energy released per fission of a uranium-235 nucleus is 190 MeV. When every atom in 47 g of pure uranium-235 undergoes fission, the energy released is α × 1023 MeV. The value of α is ______. (Avogadro number = 6 × 1023 per mole.)
Answer 228
Where it goes wrong Treating 47 g as one mole. The molar mass is 235 g, so 47 g is a fifth of a mole.
Q22 · Units and Dimensions · numeric · on the pattern of Q47
A ball of radius r and density ρ, dropped through a viscous liquid of density σ and viscosity η, reaches its terminal velocity after a time t given by t = Aρarbηcσd, where A is a dimensionless constant and a, b, c, d are integers. The value of (b + c)/(a + d) is ______.
Answer 1
Where it goes wrong Giving up because a and d cannot be found one by one. The combination asked for is exactly the one that is determined.
Q23 · Rotational Motion · numeric · on the pattern of Q48
A uniform circular disc of mass M and radius r has a concentric circular hole of radius r/2 cut out of it. The moment of inertia of what is left, about the axis of the disc, is (x/32)Mr2. The value of x is ______.
Answer 15
Where it goes wrong Using M for the mass of the removed piece as well. The hole is a quarter of the area, so it carries a quarter of the mass.
Q24 · Ray Optics · numeric · on the pattern of Q49
A thin lens forms images of the same size when the object is placed at 8 cm and at 24 cm from it. The focal length of the lens is ______ cm.
Answer 16 cm
Where it goes wrong Assuming both images must be real. One of the two is virtual, which is exactly why the sizes can match.
Q25 · Waves · numeric · on the pattern of Q50
The speed of sound in air doubles when the temperature is raised from 0 °C to α °C. The value of α is ______.
Answer 819
Where it goes wrong Doubling 0 °C, which gives nothing, or working in celsius at all. The square-root law needs absolute temperature.
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, 23 January 2026, is on its own page, and the other January dates are 21, 22, 24 and 28 January.
All shifts, date by date: JEE Main Previous Years Papers.
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