The morning shift of 23 January 2025, the third Physics paper of JEE Main 2025 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
| Exam | JEE Main 2025, Session 1 |
|---|---|
| Date | 23 January 2025 |
| Shift | Shift 1 — 9:00 AM to 12:00 PM IST |
| Paper | Paper 1 (B.E./B.Tech) |
| Physics | 25 questions — 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 |
|---|---|---|
| 1 | RC circuit at the instant the key is closed | Current Electricity |
| 2 | Magnetic field of a given electromagnetic wave | Electromagnetic Waves |
| 3 | Two samples, one decaying three times faster | Nuclei |
| 4 | Floating cube pushed down, time period | Oscillations |
| 5 | Statements about self-inductance | Electromagnetic Induction |
| 6 | Velocity-time graph, distance covered | Motion in a Straight Line |
| 7 | Sphere rolling down two different inclines | Rotational Motion |
| 8 | Circuit readings, resistance and potentials | Current Electricity |
| 9 | Spherical surface between air and glass | Ray Optics |
| 10 | Statements about a moving coil galvanometer | Moving Charges and Magnetism |
| 11 | Lens in a liquid, back surface silvered | Ray Optics |
| 12 | Hot water flow and surface tension of soap water | Mechanical Properties of Fluids |
| 13 | Charge between an axial and an equatorial dipole | Electric Charges and Fields |
| 14 | Lateral shift through a glass slab | Ray Optics |
| 15 | Lead bullet melting inside a block | Thermal Properties of Matter |
| 16 | Matter wave of a sub-atomic particle | Dual Nature of Radiation and Matter |
| 17 | Matching the four thermodynamic processes | Thermodynamics |
| 18 | Disc with a hole, centre of mass | Centre of Mass |
| 19 | Dimensions from a position-time expression | Units and Measurements |
| 20 | What the ratio of two charge densities stands for | Units and Measurements |
| 21 | Current when it is changing at a given rate | Electromagnetic Induction |
| 22 | Two vectors at right angles, find the constant | Motion in a Plane |
| 23 | Gas compressed suddenly to a quarter of its volume | Thermodynamics |
| 24 | Work done by a varying force along a path | Work, Energy and Power |
| 25 | Electrostatic force compared with gravitational force | Electric Charges and Fields |
Chapter by chapter
| Chapter | Questions | Marks |
|---|---|---|
| Ray Optics | 3 | 12 |
| Current Electricity | 2 | 8 |
| Electric Charges and Fields | 2 | 8 |
| Electromagnetic Induction | 2 | 8 |
| Thermodynamics | 2 | 8 |
| Units and Measurements | 2 | 8 |
| Centre of Mass | 1 | 4 |
| Dual Nature of Radiation and Matter | 1 | 4 |
| Electromagnetic Waves | 1 | 4 |
| Mechanical Properties of Fluids | 1 | 4 |
| Motion in a Plane | 1 | 4 |
| Motion in a Straight Line | 1 | 4 |
| Moving Charges and Magnetism | 1 | 4 |
| Nuclei | 1 | 4 |
| Oscillations | 1 | 4 |
| Rotational Motion | 1 | 4 |
| Thermal Properties of Matter | 1 | 4 |
| Work, Energy and Power | 1 | 4 |
Where the 100 marks sat
| Part of Physics | Qs | Marks | Share | Which ones |
|---|---|---|---|---|
| Electricity and magnetism | 8 | 32 | 32% | Q1, 2, 5, 8, 10, 13, 21, 25 |
| Mechanics and properties of matter | 6 | 24 | 24% | Q6, 7, 12, 18, 22, 24 |
| Optics | 3 | 12 | 12% | Q9, 11, 14 |
| Heat and thermodynamics | 3 | 12 | 12% | Q15, 17, 23 |
| Modern physics | 2 | 8 | 8% | Q3, 16 |
| Units and measurements | 2 | 8 | 8% | Q19, 20 |
| Oscillations | 1 | 4 | 4% | Q4 |
How tough it was
This shift leaned hard on statements. Five questions gave a list of claims and asked which ones hold. That is not hard physics, but it punishes half-learnt definitions, because one wrong claim takes the whole answer down with it.
Electricity and magnetism carried a third of the paper again. Optics gave three questions and all three needed a clean sign convention: the refracting surface, the silvered lens and the slab.
The slow ones were the two dipoles acting on one charge, and the silvered lens sitting in a liquid. Both reward a student who writes the standard formula first and puts the numbers in last.
Section B was fair. Three of the five are a single substitution once the right relation is chosen.
All 25 Physics questions, solved
Q1 · Current Electricity · on the pattern of Q1
An uncharged capacitor C is joined in series with a resistor R and a battery of emf E. The key is closed. At that very instant, what is the current in the circuit and the potential difference across the capacitor?
Answer Current is E/R, the largest it will ever be; the capacitor voltage is zero
Where it goes wrong Thinking a capacitor blocks current from the start. It blocks only when it is fully charged; at the first instant it behaves like a plain wire.
Q2 · Electromagnetic Waves · on the pattern of Q2
An electromagnetic wave travels through free space along the +z direction. Its electric field points along +x with amplitude 60 N/C. Find the amplitude and direction of the magnetic field. (c = 3 × 108 m/s)
Answer 2 × 10−7 T, along +y
Where it goes wrong Multiplying by c instead of dividing, or taking B along the direction of travel. B is always perpendicular to both E and the direction of travel.
Q3 · Nuclei · on the pattern of Q3
Two samples start with the same number of nuclei. The second decays with three times the decay constant of the first. After one half-life of the first sample, find the ratio of the number left in the second to that in the first.
Answer 1 : 4
Where it goes wrong Answering 1/8. That is the fraction left in the second sample, not the ratio between the two.
Q4 · Oscillations · on the pattern of Q4
A hollow cube of side 10 cm and mass 100 g floats in water. It is pushed down a little and released. Find the time period of the oscillation. (g = 10 m/s2, density of water = 1000 kg/m3)
Answer About 0.20 s
Where it goes wrong Using the volume of the cube in place of the base area. Only the face area matters, because that is what sets how much extra water is pushed aside.
Q5 · Electromagnetic Induction · on the pattern of Q5
A coil with an air core has self-inductance L. The core is replaced by a material of relative permeability 500, nothing else changing. Find the new self-inductance.
Answer 500 L
Where it goes wrong Believing inductance depends on geometry alone. Geometry and the core material both count, which is exactly why iron cores are used.
Q6 · Motion in a Straight Line · on the pattern of Q6
A vehicle starts from rest, speeds up uniformly to 40 m/s in 10 s, holds that speed for 20 s, then slows uniformly to rest in another 10 s. Find the total distance covered.
Answer 1.2 km
Where it goes wrong Multiplying the top speed by the total time. That counts the two sloping parts at full speed, which they never reach for most of their duration.
Q7 · Rotational Motion · on the pattern of Q7
A solid sphere rolls without slipping from the top of an incline of fixed length L, first when the incline is at 30° and then at 60°. Find the ratio v12 : v22 of the squared speeds at the bottom.
Answer 1 : √3
Where it goes wrong Taking the drop as L instead of L sinθ. The length of the slope is given, not the height.
Q8 · Current Electricity · on the pattern of Q8
A 12 V battery of negligible internal resistance feeds a 4 Ω resistor in series with a parallel pair of 6 Ω and 12 Ω. Find the total resistance and the current drawn.
Answer 8 Ω and 1.5 A
Where it goes wrong Adding all three resistances. Work the parallel part out first, then put it in series.
Q9 · Ray Optics · on the pattern of Q9
A spherical surface of radius R separates air from glass of refractive index 1.5, with the centre of curvature inside the glass. A point object in air forms a real image inside the glass at the same distance from the surface as the object. Find that distance.
Answer 5R
Where it goes wrong Dropping the minus sign on u. The object sits on the incoming side, so its distance is negative in the Cartesian convention.
Q10 · Moving Charges and Magnetism · on the pattern of Q10
The number of turns in a moving coil galvanometer is doubled, with the same wire, same area and same spring. What happens to its current sensitivity and to its voltage sensitivity?
Answer Current sensitivity doubles; voltage sensitivity stays the same
Where it goes wrong Assuming both sensitivities double. The extra wire brings extra resistance with it, and that is what holds the voltage sensitivity back.
Q11 · Ray Optics · on the pattern of Q11
A thin convex lens of focal length 20 cm is silvered on its back surface, whose radius of curvature is 30 cm. Find the focal length of the mirror it now behaves as.
Answer 6 cm, behaving as a concave mirror
Where it goes wrong Counting the lens power once. Light goes through the lens, reflects off the silver, and comes back through the lens, so it is counted twice.
Q12 · Mechanical Properties of Fluids · on the pattern of Q12
Two claims. One: hot water flows faster than cold water. Two: soap water has a higher surface tension than fresh water. Which are true?
Answer The first is true, the second is false
Where it goes wrong Thinking soap raises surface tension because it makes bubbles. It is the opposite — bubbles form easily precisely because the surface tension has been lowered.
Q13 · Electric Charges and Fields · on the pattern of Q13
A charge Q sits on the axis of one dipole at distance r, and at the same distance r on the equatorial line of a second, identical dipole. Compare the two forces on Q.
Answer The axial dipole pulls or pushes twice as hard, a ratio of 2 : 1
Where it goes wrong Treating the two positions as equivalent. The axial point always feels twice the field of the equatorial point at the same distance.
Q14 · Ray Optics · on the pattern of Q14
A ray enters a parallel sided glass slab of thickness h at an angle of incidence i and refracts at an angle r. Write the lateral shift of the emerging ray.
Answer h sin(i − r) / cos r
Where it goes wrong Writing h tan(i − r). That treats the slab thickness as the path length, but the ray travels a longer, slanted path inside.
Q15 · Thermal Properties of Matter · on the pattern of Q15
A lead bullet at 300 K strikes a wooden block and melts completely. Lead melts at 600 K, its specific heat is 125 J kg−1 K−1 and its latent heat of fusion is 2.5 × 104 J kg−1. If the total heat needed is 1250 J, find the mass of the bullet.
Answer 20 g
Where it goes wrong Leaving out the latent heat. Melting takes heat at a fixed temperature, and here it is nearly half the total.
Q16 · Dual Nature of Radiation and Matter · on the pattern of Q16
A particle of mass 10−30 kg moves at 6.63 × 105 m/s. Find its de Broglie wavelength and say which part of the spectrum it matches. (h = 6.63 × 10−34 J s)
Answer 1 nm, which is the X-ray range
Where it goes wrong Using energy instead of momentum. The de Broglie relation needs mv, not ½mv2.
Q17 · Thermodynamics · on the pattern of Q17
Match each description with its process: (a) temperature held fixed, (b) no heat enters or leaves, (c) no work done, (d) pressure held fixed.
Answer (a) isothermal, (b) adiabatic, (c) isochoric, (d) isobaric
Where it goes wrong Mixing up adiabatic and isochoric. One has no heat flow, the other has no work. They are different things.
Q18 · Centre of Mass · on the pattern of Q18
A uniform disc of radius 30 cm has a hole of radius 10 cm cut out, placed so that the edge of the hole just touches the edge of the disc. How far from the centre of the original disc is the centre of mass of what remains?
Answer 2.5 cm, on the side away from the hole
Where it goes wrong Using the ratio of radii, 1/3, for the mass of the hole. Area goes with the square of the radius, so it is 1/9.
Q19 · Units and Measurements · on the pattern of Q19
The position of a particle is x(t) = A sinωt + B cosωt + Ct + D. Find the dimensions of ABC/D.
Answer [L2 T−1]
Where it goes wrong Giving ωt a dimension. The argument of a sine must be a pure number, which is what fixes ω as one over time.
Q20 · Units and Measurements · on the pattern of Q20
λ is a linear charge density and σ is a surface charge density. What does λ/σ stand for dimensionally?
Answer A length
Where it goes wrong Calling it an area. Work the units through slowly: (C/m) ÷ (C/m2) = m.
Q21 · Electromagnetic Induction · on the pattern of Q21
A coil of inductance 3 H and resistance 12 Ω is connected to a 60 V source. At an instant the current is changing at 8 A/s. Find the current at that instant.
Answer 3 A
Where it goes wrong Writing I = E/R = 5 A. That is only the final steady current, after the current has stopped changing.
Q22 · Motion in a Plane · on the pattern of Q22
The vectors A = 2î + 3nĵ + 2k̂ and B = 2î − 2ĵ + 4k̂ are at right angles to each other. Find n.
Answer n = 2
Where it goes wrong Setting the magnitudes equal instead. Equal length and perpendicular are two different conditions.
Q23 · Thermodynamics · on the pattern of Q23
An ideal gas at 0 °C is compressed suddenly to one fourth of its volume. For this gas the ratio of specific heats is 3/2. Find the final temperature.
Answer 546 K, a rise of 273 K
Where it goes wrong Using PV = constant. That is the isothermal law and it applies to a slow squeeze, not a sudden one.
Q24 · Work, Energy and Power · on the pattern of Q24
A force F = (2xî + 3ĵ) N acts on a particle which moves from (0, 0) to (2 m, 4 m). Find the work done.
Answer 16 J
Where it goes wrong Multiplying force by distance. The x component changes along the path, so it must be integrated, not multiplied.
Q25 · Electric Charges and Fields · on the pattern of Q25
Two particles carry charges 1.6 × 10−19 C and 3.2 × 10−19 C, with masses 1 × 10−27 kg and 4 × 10−27 kg. Find the ratio of the electrostatic force between them to the gravitational force. (k = 9 × 109, G = 6.67 × 10−11 SI units)
Answer About 1.7 × 1036
Where it goes wrong Looking for the separation in the question. It is not needed, because it cancels, and that is the point the question is making.
The official paper and answer key
NTA publishes the question papers and the final answer key for each session on its own site. Always check against that file, not a coaching copy: jeemain.nta.nic.in.
Everything above is written by AcceleratePhysics. We do not reprint NTA’s question wording or its answer key on this page.
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25 questions · 45 minutes · out of 100 · +4 / −1 / 0 · score card at the end
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