The morning paper of 28 January 2026, the ninth 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 1 — 9:00 AM to 12:00 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 | Closed cycle on a p-V diagram — the net work done | Thermodynamics |
| 27 | Temperature against heat supplied for water from −20 °C to 120 °C | Thermal Properties of Matter |
| 28 | Drops falling at equal intervals — height of the fourth when the first lands | Motion in a Straight Line |
| 29 | Ice at −10 °C added to water — how much the water cools | Thermal Properties of Matter |
| 30 | Two statements on how a wavefront changes at a prism and at a pinhole | Wave Optics |
| 31 | Two cells giving the same current in series and in parallel — the internal resistance | Current Electricity |
| 32 | Current rising linearly over one period — its r.m.s. value | Alternating Current |
| 33 | Two discs joined by a rod — angular acceleration under a given torque | Rotational Motion |
| 34 | Two wires stretched equally by the same load — ratio of their Young’s moduli | Mechanical Properties of Solids |
| 35 | Work to bring a third charge to the free corner of a triangle | Electrostatic Potential and Capacitance |
| 36 | Three parallel current-carrying wires — force on 15 cm of the middle one | Moving Charges and Magnetism |
| 37 | Nucleus that absorbs protons and neutrons — growth in its surface area | Nuclei |
| 38 | Potentiometer balance with two different shunts — internal resistance of the cell | Current Electricity |
| 39 | Current through a silicon diode with a 0.7 V forward drop | Semiconductor Electronics |
| 40 | Falling body in a medium with resistance proportional to speed — the v-t graph | Laws of Motion |
| 41 | Block on a rough incline — force needed to bring it down at steady speed | Laws of Motion |
| 42 | Vernier callipers with a zero error — the corrected length | Units and Measurements |
| 43 | Biconvex and plano-concave lenses of equal power — ratio of the two radii | Ray Optics |
| 44 | Refractive index of a medium from the wave equation | Electromagnetic Waves |
| 45 | Field on the axis of a loop at a distance √3R from its centre | Moving Charges and Magnetism |
| 46 | numeric de Broglie wavelengths of a deuteron and an alpha particle compared | Dual Nature of Radiation and Matter |
| 47 | numeric Convex lens dipped in water — change in its focal length | Ray Optics |
| 48 | numeric Equivalent resistance of the given network between two points | Current Electricity |
| 49 | numeric First instant at which the potential energy of an oscillator is greatest | Oscillations |
| 50 | numeric Radius of gyration of a sphere about an axis away from its centre | Rotational Motion |
Chapter by chapter
| Chapter | Questions | Marks |
|---|---|---|
| Current Electricity | 3 | 12 |
| Laws of Motion | 2 | 8 |
| Moving Charges and Magnetism | 2 | 8 |
| Ray Optics | 2 | 8 |
| Rotational Motion | 2 | 8 |
| Thermal Properties of Matter | 2 | 8 |
| Alternating Current | 1 | 4 |
| Dual Nature of Radiation and Matter | 1 | 4 |
| Electromagnetic Waves | 1 | 4 |
| Electrostatic Potential and Capacitance | 1 | 4 |
| Mechanical Properties of Solids | 1 | 4 |
| Motion in a Straight Line | 1 | 4 |
| Nuclei | 1 | 4 |
| Oscillations | 1 | 4 |
| Semiconductor Electronics | 1 | 4 |
| Thermodynamics | 1 | 4 |
| Units and Measurements | 1 | 4 |
| Wave Optics | 1 | 4 |
All 19 shifts of JEE Main 2026, counted together chapter by chapter: JEE Main Physics important chapters.
Eighteen chapters, and Current Electricity again took three questions for 12 marks — two cells, a potentiometer and a resistor network. Together with 24 January Shift 2 these were the two January shifts where circuits paid best.
Where the 100 marks sat
| Part of Physics | Questions | Marks | Share |
|---|---|---|---|
| Electrodynamics | 8 | 32 | 32% |
| 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 | 1 | 4 | 4% |
Electrodynamics 32 for the fourth time in January. Four of the ten January shifts put exactly 32 marks there, and none put fewer than 28.
How tough it was
| Level | Questions | Share | Which ones |
|---|---|---|---|
| Straight recall or one step | 7 | 28% | 30, 32, 35, 44, 45, 46, 49 |
| Two or three steps | 12 | 48% | 28, 31, 34, 37, 38, 39, 41, 42, 43, 47, 48, 50 |
| Long or awkward | 6 | 24% | 26, 27, 29, 33, 36, 40 |
The ice-and-water calorimetry was the longest single calculation in January: the ice has to be warmed, then melted, then the melt water warmed, all against the heat the 100 kg of water gives up. Four separate terms, and a sign slip anywhere gives a plausible wrong answer.
All 25 Physics questions, solved
Q1 · Thermodynamics · on the pattern of Q26
A gas is taken round a closed rectangular cycle on the p-V diagram: an expansion from V1 to V2 at constant pressure P, a fall to pressure P/2 at constant volume, a compression back to V1 at that pressure, and a rise back to P at constant volume. The net work done in the cycle is ______.
Answer (P/2)(V2 − V1), done by the gas
Where it goes wrong Adding the areas under all four legs as positive. The expansion counts positive and the compression negative, which is exactly why only the enclosed area is left.
Q2 · Thermal Properties of Matter · on the pattern of Q27
Water is heated steadily from −20 °C to 120 °C. Describe how a graph of its temperature against the heat supplied looks.
Answer a steep rise, a flat step at 0 °C, a shallower rise, a long flat step at 100 °C, then a steep rise again
Where it goes wrong Drawing the two flat steps the same length. The boiling step is far longer than the melting one, and that difference is the point of the question.
Q3 · Motion in a Straight Line · on the pattern of Q28
Drops fall from a tap at equal intervals of time onto a floor 5 m below. The first drop strikes the floor at the very instant the sixth drop begins to fall. At that instant the fourth drop is ______ m above the ground. (g = 10 m/s2.)
Answer 4.2 m
Where it goes wrong Dividing the second by 6 instead of 5. Six drops in the air means five gaps between them.
Q4 · Thermal Properties of Matter · on the pattern of Q29
10 kg of ice at −10 °C is added to 100 kg of water at 25 °C, with no heat lost to the surroundings. The temperature of the water falls by ______ °C. (Specific heat of ice 2100 J/kg·°C, of water 4200 J/kg·°C, latent heat of fusion of ice 3.36 × 105 J/kg.)
Answer 10 °C — it settles at 15 °C
Where it goes wrong Forgetting the melt water. Once the ice has melted, those 10 kg must also be warmed from 0 °C to the final temperature, and that term is easy to leave out.
Q5 · Wave Optics · on the pattern of Q30
Two statements. Statement I: a plane wave stays plane after passing through a prism, but may become spherical after passing through a small pinhole. Statement II: the curvature of the spherical wave coming out of a slit increases as the slit is made wider. Which is true?
Answer Statement I is true, Statement II is false
Where it goes wrong Reading “wider slit, more light, more spreading”. More light gets through, but it spreads less; diffraction grows as the opening shrinks.
Q6 · Current Electricity · on the pattern of Q31
Two cells of the same emf E and the same internal resistance r are connected to an external 6 Ω resistor, and the current through it comes out the same whether the cells are in series or in parallel. The value of r is ______ Ω.
Answer 6 Ω
Where it goes wrong Doubling the emf in the parallel case too. Cells in parallel share the current, not the voltage.
Q7 · Alternating Current · on the pattern of Q32
A current rises linearly with time as i = i0t/T over the period from t = 0 to t = T. Its r.m.s. value over that period is ______.
Answer i0/√3
Where it goes wrong Reaching for i0/√2 by habit. The √2 comes from the average of sin2; a different waveform gives a different factor, and here it is √3.
Q8 · Rotational Motion · on the pattern of Q33
Two circular discs, each of mass 600 g and radius 10 cm, are joined at their centres by a light rod 30 cm long, and the whole thing turns about the common axis of the discs. A torque of (4/3) × 105 dyne·cm is applied. The angular acceleration is about ______ rad/s2.
Answer about 2.2 rad/s2
Where it goes wrong Treating 1 dyne·cm as 10−5 N·m. The dyne contributes 10−5 and the centimetre another 10−2, so the two together give 10−7.
Q9 · Mechanical Properties of Solids · on the pattern of Q34
Two wires A and B of different materials, of lengths 6.0 cm and 5.4 cm and cross-sections 3.0 × 10−5 m2 and 4.5 × 10−5 m2, stretch by the same amount under the same load. The ratio of the Young’s modulus of A to that of B is x : 3. The value of x is ______.
Answer 5
Where it goes wrong Converting the lengths to metres and the areas not at all, or the other way round. Here only the ratio matters, so the centimetres cancel — but the two lengths must be in the same unit as each other.
Q10 · Electrostatic Potential · on the pattern of Q35
Charges of 1 nC and 2 nC sit at two corners of an equilateral triangle of side 3 cm. The work done in bringing a 3 nC charge from infinity to the third corner is ______ μJ. (1/4πε0 = 9 × 109 N·m2/C2.)
Answer 2.7 μJ
Where it goes wrong Working out forces and trying to combine them as vectors. The work only needs the potential, which is a single number.
Q11 · Moving Charges and Magnetism · on the pattern of Q36
Three long straight parallel wires P, Q and R lie in one plane, each carrying 10 A. Q is 2 cm from P and 4 cm from R, with P and R on opposite sides of it. P and R carry current in the same direction and Q in the opposite direction. The force on a 15 cm length of Q is ______ N. (μ0 = 4π × 10−7 T·m/A.)
Answer 7.5 × 10−5 N, away from P
Where it goes wrong Adding the two forces. P and R are on opposite sides, so their pushes on Q oppose each other and the nearer wire wins.
Q12 · Nuclei · on the pattern of Q37
A nucleus with mass number 8 is bombarded and absorbs 10 electrons, 10 protons and 9 neutrons. The surface area of the nucleus grows by ______ per cent.
Answer 125% (the new area is 225% of the old)
Where it goes wrong Counting the 10 electrons into the mass number, or using A1/3 instead of A2/3 for the area.
Q13 · Current Electricity · on the pattern of Q38
On a potentiometer, when the cell in the secondary circuit is shunted with 4 Ω the balance length is 120 cm, and when it is shunted with 12 Ω the balance length is 180 cm. The internal resistance of the cell is ______ Ω.
Answer 4 Ω
Where it goes wrong Using the usual r = R(l1/l2 − 1), which needs one open-circuit length. Here both readings are with shunts, so the two equations have to be divided.
Q14 · Semiconductor Electronics · on the pattern of Q39
A silicon diode, which drops 0.7 V when forward biased, is put in series with a 1 kΩ resistor across a 12 V battery. The current through the diode is ______ mA.
Answer 11.3 mA
Where it goes wrong Using the whole 12 V across the resistor and answering 12 mA. The 0.7 V is the whole reason the question mentions silicon.
Q15 · Laws of Motion · on the pattern of Q40
A particle of mass m falls from rest through a medium whose resistive force is F = −kv, with v the speed and k a constant. Describe the graph of velocity against time.
Answer it starts at zero with slope g and curves over, flattening out at the terminal speed mg/k
Where it goes wrong Drawing a straight line, or a curve that starts flat. The slope is largest at the very start, when there is no resistance yet, and shrinks from there.
Q16 · Laws of Motion · on the pattern of Q41
A block of mass 5 kg is on a plane inclined at 30° to the horizontal, with a coefficient of friction 2/√3 between them. The force that must be applied so the block slides down at a steady speed is ______ N. (g = 10 m/s2.)
Answer 25 N, applied down the slope
Where it goes wrong Assuming the push must be up the slope to control the block. With this much friction the block needs help to get moving at all, so the force goes downhill.
Q17 · Units and Measurement · on the pattern of Q42
With the jaws of a vernier calliper closed, the zero of the vernier scale lies to the right of the zero of the main scale and the 4th vernier mark coincides with a main scale mark. Measuring a cylinder, the main scale reads 15 divisions and the 5th vernier division coincides with a main scale mark. The length of the cylinder is ______ mm. (Least count = 0.1 mm, 1 main scale division = 1 mm.)
Answer 15.1 mm
Where it goes wrong Adding the 0.4 mm. “To the right” means the jaws already show a reading with nothing between them, so that much must come off.
Q18 · Ray Optics · on the pattern of Q43
A biconvex lens of refractive index 1.5 and a plano-concave lens of refractive index 1.7 have powers of equal magnitude. The curved face of the plano-concave lens has exactly the same radius as the back surface of the biconvex lens. The ratio of the front to the back radius of the biconvex lens is ______.
Answer 5 : 2
Where it goes wrong Writing the biconvex power as (n − 1)(1/R1 − 1/R2) with both radii positive. For a biconvex lens the two centres of curvature are on opposite sides, so the two terms add.
Q19 · Electromagnetic Waves · on the pattern of Q44
The electric field of an electromagnetic wave in a medium is E(x, t) = 25 sin(2.0 × 1015t − 107x), in SI units. The refractive index of the medium is ______.
Answer 1.5
Where it goes wrong Treating 2.0 × 1015 as a frequency rather than an angular frequency. It does not matter here, since the 2π cancels in ω/k, but it does if the wavelength is asked for.
Q20 · Moving Charges and Magnetism · on the pattern of Q45
The magnetic field at the centre of a circular current-carrying loop of radius R is 16 μT. The field at a point on the axis a distance √3R from the centre is ______ μT.
Answer 2 μT
Where it goes wrong Using an inverse square instead of the 3/2 power. The axial formula falls off faster than that near the loop, and the √3 is chosen so that the bracket comes out exactly 4R2.
Q21 · Dual Nature of Matter · numeric · on the pattern of Q46
The ratio of the de Broglie wavelength of a deuteron of kinetic energy E to that of an alpha particle of kinetic energy 2E is n : 1. The value of n is ______. (Take the proton and neutron masses as equal.)
Answer 2
Where it goes wrong Forgetting that the alpha particle has both four times the mass and twice the energy. Each of those shrinks its wavelength, and together they give the factor of two.
Q22 · Ray Optics · numeric · on the pattern of Q47
A convex lens of refractive index 1.5 has focal length f = 18 cm in air. It is immersed in water of refractive index 4/3. The difference between its focal lengths in water and in air is α × f. The value of α is ______.
Answer 3
Where it goes wrong Using 1.5 − 4/3 for the bracket. It is the ratio of the indices that goes in, not their difference.
Q23 · Current Electricity · numeric · on the pattern of Q48
Resistors of 1 Ω, 2 Ω and 3 Ω are all joined in parallel between the points A and B. The equivalent resistance is x/11 Ω. The value of x is ______.
Answer 6
Where it goes wrong Forgetting to invert at the end and giving 11/6. A quick sanity check settles it: the answer has to be below 1 Ω.
Q24 · Oscillations · numeric · on the pattern of Q49
A particle in simple harmonic motion of period T has displacement x(t) = A sinωt. Its potential energy first reaches its greatest value at t = T/2β. The value of β is ______.
Answer 2
Where it goes wrong Answering t = T/2, where the particle passes through the centre again. That is where the potential energy is least, not greatest.
Q25 · Rotational Motion · numeric · on the pattern of Q50
A solid sphere of radius 10 cm turns about an axis 15 cm from its centre. Its radius of gyration about that axis is n cm. The value of n is about ______.
Answer √265, about 16.3 cm
Where it goes wrong Adding 10 and 15 to get 25 cm, or using (2/5)R2 alone. The radius of gyration is a root-mean-square distance, so the two contributions add as squares.
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. The other January 2026 dates were 21, 22, 23 and 24 January, two shifts on each.
All shifts, date by date: JEE Main Previous Years Papers.
Sit a paper in the same shape, free
25 questions. 45 minutes. Out of 100. Marked the way JEE Main marks it, with a hint and the answer key for every question you miss. No payment, no card, and no account needed to start.
Reading a past paper tells you what was asked. Sitting one on the clock tells you what you can do. Only the second one moves your score.