The afternoon shift of 22 January 2025, the second 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 | 22 January 2025 |
| Shift | Shift 2 — 3:00 PM to 6:00 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 | Electron circling in a magnetic field with Bohr’s condition | Moving Charges and Magnetism |
| 2 | Body in a vertical circle, kinetic energy at two points | Work, Energy and Power |
| 3 | Biconvex lens cut into four parts, power of a piece | Ray Optics |
| 4 | Torque of a force about the origin | Rotational Motion |
| 5 | Work done is zero, find the missing component | Work, Energy and Power |
| 6 | Thin film coated on glass, thickness for best transmission | Wave Optics |
| 7 | Dimensional formula of capacitance | Units and Measurements |
| 8 | Series LCR at resonance when the resistance doubles | Alternating Current |
| 9 | Ball falling in glycerine, viscous force at steady speed | Mechanical Properties of Fluids |
| 10 | Percentage error in the density of a wire | Units and Measurements |
| 11 | Which thermodynamic variables are extensive | Thermodynamics |
| 12 | Tube narrowing, speed of water at the exit | Mechanical Properties of Fluids |
| 13 | Red and blue fringes in a double slit | Wave Optics |
| 14 | Projectile, loss of kinetic energy up to the top | Work, Energy and Power |
| 15 | Which gate fits the given truth table | Semiconductor Electronics |
| 16 | Photoelectric effect when the wavelength is halved | Dual Nature of Radiation and Matter |
| 17 | Pendulum carried to a heavier, bigger planet | Oscillations |
| 18 | Ratio of specific heats with and without vibration | Kinetic Theory of Gases |
| 19 | Short dipole, potential and field off the axis | Electric Charges and Fields |
| 20 | Loop leaving a field, emf against time | Electromagnetic Induction |
| 21 | Displacement current through part of a capacitor gap | Electromagnetic Waves |
| 22 | Proton in crossed fields, then in a circle | Moving Charges and Magnetism |
| 23 | Liquid filled tube spun about one end, force at the far end | Laws of Motion |
| 24 | Net current drawn by the given circuit | Current Electricity |
| 25 | Two parallel wires carrying opposite currents | Moving Charges and Magnetism |
Chapter by chapter
| Chapter | Questions | Marks |
|---|---|---|
| Moving Charges and Magnetism | 3 | 12 |
| Work, Energy and Power | 3 | 12 |
| Mechanical Properties of Fluids | 2 | 8 |
| Units and Measurements | 2 | 8 |
| Wave Optics | 2 | 8 |
| Alternating Current | 1 | 4 |
| Current Electricity | 1 | 4 |
| Dual Nature of Radiation and Matter | 1 | 4 |
| Electric Charges and Fields | 1 | 4 |
| Electromagnetic Induction | 1 | 4 |
| Electromagnetic Waves | 1 | 4 |
| Kinetic Theory of Gases | 1 | 4 |
| Laws of Motion | 1 | 4 |
| Oscillations | 1 | 4 |
| Ray Optics | 1 | 4 |
| Rotational Motion | 1 | 4 |
| Semiconductor Electronics | 1 | 4 |
| Thermodynamics | 1 | 4 |
Where the 100 marks sat
| Part of Physics | Qs | Marks | Share | Which ones |
|---|---|---|---|---|
| Electricity and magnetism | 8 | 32 | 32% | Q1, 8, 19, 20, 21, 22, 24, 25 |
| Mechanics and properties of matter | 7 | 28 | 28% | Q2, 4, 5, 9, 12, 14, 23 |
| Optics | 3 | 12 | 12% | Q3, 6, 13 |
| Heat and thermodynamics | 2 | 8 | 8% | Q11, 18 |
| Modern physics and electronics | 2 | 8 | 8% | Q15, 16 |
| Units and measurements | 2 | 8 | 8% | Q7, 10 |
| Oscillations | 1 | 4 | 4% | Q17 |
How tough it was
The afternoon paper of the same day went wider than the morning one. Eighteen chapters in 25 questions, and almost a third of the paper sat in electricity and magnetism.
Four questions were pure recall of a definition — extensive and intensive variables, the truth table, the dimensional formula and the fringe comparison. Those are the marks you should never lose.
The slow ones were the cut lens, the dipole off the axis and the spinning tube of liquid. All three punish a student who reaches for a formula before drawing the picture. The spinning tube in particular cannot be done by putting the whole mass at the far end.
Section B was straightforward arithmetic once the right relation was written down.
All 25 Physics questions, solved
Q1 · Moving Charges and Magnetism · on the pattern of Q1
An electron moves in a circle in a plane perpendicular to a uniform magnetic field B. If Bohr’s condition mvr = nh/2π is taken to hold, find the radius of the n-th orbit.
Answer r = √(nh / 2πeB)
Where it goes wrong Using r = nh/(2πmv) and stopping there. The speed is not given, so mv has to be replaced using the magnetic condition first.
Q2 · Work, Energy and Power · on the pattern of Q2
A body of mass 200 g moves in a vertical circle of radius 1 m. Its speed at the lowest point is 8 m/s. Find the ratio of its kinetic energy at the lowest point to that at the highest point. (g = 10 m/s2)
Answer 8 : 3
Where it goes wrong Using R instead of 2R for the height. The top of the circle is two radii above the bottom.
Q3 · Ray Optics · on the pattern of Q3
A thin symmetric biconvex lens of power 5 D is cut into two equal halves by a plane that contains the principal axis. Find the power of each half.
Answer 5 D, unchanged
Where it goes wrong Assuming the power halves. That happens only when the cut is across the axis, which turns the lens into two plano-convex lenses.
Q4 · Rotational Motion · on the pattern of Q4
A force F = (î + 2ĵ + 3k̂) N acts on a particle whose position vector is r = (2î + ĵ) m. Find the torque about the origin.
Answer (3î − 6ĵ + 3k̂) N m
Where it goes wrong Writing F × r. The order matters and reverses every sign.
Q5 · Work, Energy and Power · on the pattern of Q5
A force F = (3î + bĵ + 2k̂) N acts on a particle which is displaced by (2î − ĵ + k̂) m. Find b if the work done is zero.
Answer b = 8
Where it goes wrong Dropping the minus sign in the displacement. One wrong sign here flips the answer completely.
Q6 · Wave Optics · on the pattern of Q6
A film of refractive index 1.38 is coated on glass of refractive index 1.52 so that light of wavelength 552 nm is reflected as little as possible. Find the smallest thickness of the film.
Answer 100 nm
Where it goes wrong Using t = λ/2μ. That is the rule when only one of the two reflections flips phase, which depends on the refractive index of the glass underneath.
Q7 · Units and Measurements · on the pattern of Q7
Write the dimensional formula of capacitance in terms of M, L, T and charge Q.
Answer [M−1 L−2 T2 Q2]
Where it goes wrong Forgetting that potential already carries a charge in its denominator, so the charge ends up squared.
Q8 · Alternating Current · on the pattern of Q8
In a series LCR circuit driven at resonance the current amplitude is I0. The resistance is now made three times larger, with L, C and the source unchanged. Find the new current amplitude at resonance.
Answer I0/3
Where it goes wrong Trying to bring L and C into the answer. At resonance they cancel exactly, which is the whole point of resonance.
Q9 · Mechanical Properties of Fluids · on the pattern of Q9
A solid ball of mass M is dropped into a tall jar of liquid whose density is one third that of the ball. After it reaches a steady speed, find the viscous force on the ball.
Answer 2Mg/3
Where it goes wrong Writing Mg for the viscous force. Buoyancy is already carrying part of the weight.
Q10 · Units and Measurements · on the pattern of Q10
The density of a wire is found from mass (0.80 ± 0.004) g, radius (0.40 ± 0.01) cm and length (20.00 ± 0.10) cm. Find the maximum percentage error in the density.
Answer 6 per cent
Where it goes wrong Leaving out the factor of 2 on the radius. The radius is squared in the formula, so its error counts twice.
Q11 · Thermodynamics · on the pattern of Q11
Of volume, density, internal energy and temperature, which are extensive and which are intensive?
Answer Volume and internal energy are extensive; density and temperature are intensive
Where it goes wrong Calling density extensive because mass is. Any ratio of two extensive quantities comes out intensive.
Q12 · Mechanical Properties of Fluids · on the pattern of Q12
Water enters the wide part of a pipe of radius 3 cm at 2 m/s and leaves through a narrow part of radius 1 cm. Find the speed at the exit.
Answer 18 m/s
Where it goes wrong Using the ratio of radii without squaring, which gives 6 m/s.
Q13 · Wave Optics · on the pattern of Q13
The same double slit set-up is lit first by blue light of 450 nm and then by red light of 650 nm. Which gives wider fringes, and by what factor?
Answer Red, wider by 13/9, about 1.44 times
Where it goes wrong Saying red fringes are closer. A bigger wavelength spreads the pattern out, it does not squeeze it.
Q14 · Work, Energy and Power · on the pattern of Q14
A ball of mass 200 g is projected at 30 m/s at 60° to the horizontal. Find the loss in its kinetic energy by the time it reaches the highest point.
Answer 67.5 J
Where it goes wrong Taking the kinetic energy at the top as zero. The ball still moves horizontally there; only the vertical part dies.
Q15 · Semiconductor Electronics · on the pattern of Q15
A gate gives an output of 1 only when both of its inputs are 0. Name the gate.
Answer NOR gate
Where it goes wrong Choosing NAND. NAND gives 0 only when both inputs are 1, which is the mirror image of this.
Q16 · Dual Nature of Radiation and Matter · on the pattern of Q16
Light of wavelength λ falling on a metal of work function 2 eV ejects electrons of maximum kinetic energy 3 eV. Find the maximum kinetic energy when light of wavelength λ/2 is used.
Answer 8 eV
Where it goes wrong Doubling the kinetic energy to 6 eV. It is the photon energy that doubles, and the work function is subtracted only once.
Q17 · Oscillations · on the pattern of Q17
A simple pendulum is taken to a planet whose mass is 9 times and radius 3 times that of the Earth. What happens to its time period?
Answer It stays the same
Where it goes wrong Bringing the mass of the bob into it. The bob mass cancels out of the period formula altogether.
Q18 · Kinetic Theory of Gases · on the pattern of Q18
For a rigid diatomic gas the ratio of specific heats is γ1. For a diatomic gas that also has a vibrational mode active, it is γ2. Compare them.
Answer γ2 is smaller than γ1
Where it goes wrong Assuming more ways to store energy means a bigger γ. Extra modes raise Cv, and γ = 1 + R/Cv falls towards 1.
Q19 · Electric Charges and Fields · on the pattern of Q19
A short dipole sits at the origin with its moment along the x axis. At a point on the x axis at distance r the potential is V0 and the field is E0. Find the potential and the field at a point on the y axis at distance 2r.
Answer Potential zero, field E0/16
Where it goes wrong Halving V0 instead of writing zero. The equatorial potential of a dipole is zero at every distance, not just far away.
Q20 · Electromagnetic Induction · on the pattern of Q20
A rectangular loop is pulled out of a uniform magnetic field at a constant speed. Describe how the induced emf behaves with time while the loop is partly inside the field.
Answer It stays constant while the loop is leaving, then drops to zero
Where it goes wrong Expecting the emf to tail off slowly. The rate of change of area is fixed by the speed, not by how much is left inside.
Q21 · Electromagnetic Waves · on the pattern of Q21
A parallel plate capacitor of plate area 20 cm2 is being charged by a current of 4 A. Find the displacement current through a flat surface of area 5 cm2 drawn inside the gap, parallel to the plates.
Answer 1 A
Where it goes wrong Taking the whole 4 A through the smaller surface. Only the share of the area counts.
Q22 · Moving Charges and Magnetism · on the pattern of Q22
A proton moves undeflected at 3 × 105 m/s through crossed electric and magnetic fields. When the electric field is switched off, it moves in a circle of radius 3 cm. Find the electric field. (m = 1.6 × 10−27 kg, e = 1.6 × 10−19 C)
Answer 3 × 104 N/C
Where it goes wrong Starting with the electric field. The radius gives B first, and only then does E = vB follow.
Q23 · Laws of Motion · on the pattern of Q23
A tube of length 2 m, closed at both ends and filled with a liquid of total mass 3M, is spun in a horizontal plane about one of its ends with angular velocity ω. Find the force the liquid exerts on the far end.
Answer 3Mω2
Where it goes wrong Putting the whole mass at the far end, which doubles the answer. The liquid near the axis needs much less force, so the average works out at L/2.
Q24 · Current Electricity · on the pattern of Q24
A 12 V battery of negligible internal resistance is connected across a 6 Ω and a 12 Ω resistor joined in parallel. Find the current drawn from the battery.
Answer 3 A
Where it goes wrong Adding the resistances as if in series. In parallel the total is always smaller than the smaller one.
Q25 · Moving Charges and Magnetism · on the pattern of Q25
Two long parallel wires 10 cm apart carry 6 A and 4 A in opposite directions. Find the magnetic field at a point on the line joining them, 5 cm beyond the 4 A wire. (μ0 = 4π × 10−7 SI units)
Answer 8 × 10−6 T
Where it goes wrong Adding the two magnitudes. For opposite currents the fields add only between the wires, and subtract outside them.
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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