Physics · JEE Main syllabus unit

Experimental Skills: Virtual Labs

JEE Main has a full syllabus unit on experiments. Practise them here: take readings, plot the graph, find the result, then test yourself with viva questions.

Last updated: 26 October 2026

Direct answer

Experimental Skills is an official JEE Main Physics unit, and 1–2 questions on it are common.

Each lab has a Notebook tab. Record readings, plot any two columns and download them as a CSV file, just like a practical file.

Labs

Experiments you can do here

Experiment	Lab	What to record
Simple pendulum: find g	Simple pendulum lab	Record T for 5 lengths, plot T² against L; slope = 4π²/g.
Metre bridge: unknown resistance	Metre bridge lab	Find the null point for 3–4 values of R, then average X = R·l/(100 − l).
Resonance tube: speed of sound	Resonance tube lab	Find L₁ and L₂ for one fork, then v = 2f(L₂ − L₁).
Convex lens: focal length (u–v method)	Lens lab · 3D ray tracing	Record u and v for 5 positions, plot 1/v against 1/u; intercepts give 1/f.
Vernier callipers and screw gauge	Vernier and screw gauge lab	Find least count and zero error first, then take 3 readings and average.
Ohm's law: resistance and resistivity	Ohm's law lab	Plot V against I; slope = R. Use ρ = RA/l for resistivity.
Young's modulus, viscosity, surface tension	Stress–strain lab · Fluids lab	Know the formula, the graph and the main source of error for each.
Semiconductor diode characteristics	Diode lab	Forward: knee voltage ≈ 0.7 V (Si). Reverse: tiny current until breakdown.

Method

How to use the notebook

Set up the experiment and press Record reading.
Change one quantity only, then record again. Take at least five readings.
Choose the x and y columns to see the graph. A straight line means you chose the right pair (for example T² against L).
Download the CSV to keep your readings.

Viva

Viva questions with answers

Simple pendulum: viva questions

Why is the amplitude kept small? — T = 2π√(L/g) holds only for small angles; at 60° the period is about 7% longer.
What is the effective length? — From the point of suspension to the centre of the bob: L = thread length + bob radius.
Why plot T² against L? — It is a straight line through the origin, so g comes from the slope (4π²/g) and random errors average out.
Why time 20 oscillations, not one? — The reaction-time error (≈0.2 s) is shared over 20 periods, cutting the percentage error 20 times.

Metre bridge: viva questions

Why is the null point kept near the middle? — End corrections and the percentage error in l are smallest there.
Why interchange R and X? — It cancels the end-error and a non-uniform-wire error when the two results are averaged.
Why is the bridge wire made of manganin or constantan? — Low temperature coefficient of resistance and high resistivity.
Why use thick copper strips? — Their resistance is negligible, so only the wire lengths matter.

Resonance tube: viva questions

Why is L₂ − L₁ used? — The end correction e cancels: L₁ + e = λ/4 and L₂ + e = 3λ/4.
What is the end correction? — About 0.3d (d = inner diameter), because the antinode forms slightly outside the open end.
Why is the second resonance fainter? — The air column is longer, so more energy is lost before the reflected wave returns.

Vernier and screw gauge: viva questions

What is least count? — The smallest length an instrument can measure: 1 MSD − 1 VSD for a vernier, pitch ÷ number of circular divisions for a screw gauge.
How is zero error corrected? — Corrected reading = observed reading − zero error (zero error is positive if the zero lies above the reference line).
What is backlash error? — Lost motion in a worn screw; always turn the screw in one direction while measuring.

Error analysis

Main errors and how to reduce them

Experiment	Main error	How to reduce it
Simple pendulum	Reaction time in starting/stopping the watch	Time 20–30 oscillations; start counting at the mean position
Metre bridge	End error and non-uniform wire	Keep null point near 50 cm; interchange R and X and average
Resonance tube	End correction; judging the loudest point	Use L₂ − L₁; approach resonance from both sides
u–v method	Parallax in locating the image	Remove parallax tip to tip; use index correction
Screw gauge	Zero error and backlash	Find zero error first; turn in one direction only
Ohm's law	Heating of the wire changes R	Pass current only while reading; use small currents

PYQs

How JEE asks about experiments

Questions on experiments in JEE Main usually test: least count and zero error, which graph is a straight line, the percentage error in a result (ΔZ/Z = p·ΔA/A + q·ΔB/B …), and the reason behind a precaution. Practise them in the Units, Dimensions and Errors PYQs and the Experimental Skills notes.

Real JEE Main 2026 experiment questions (verified answers and step-by-step solutions on the linked page):

2 April 2026 Shift 2, Q32: In a screw gauge the zero of main scale reference line coincides with the fifth division of the circular scale when two studs are in contact. There are 100 divisions in c…
4 April 2026 Shift 1, Q26: In a screw gauge when the circular scale is given five complete rotations it moves linearly by 2.5 mm. If the circular scale has 100 divisions, the least count of screw g…
5 April 2026 Shift 1, Q26: In a Vernier calipers, when both jaws touch each other, zero of the Vernier scale is shifted to the right of zero of the main scale and 7^th Vernier division coincides wi…
6 April 2026 Shift 2, Q33: Figure represents the extension (\Delta l) of a wire of length 1 meter, suspended from the ceiling of the room at one end with a load W connected to the other end. If the…

FAQs

Frequently asked questions

Which experiments are in the JEE Main syllabus?

The official list includes the simple pendulum, metre bridge, resonance tube, focal length by u–v method, Ohm's law, Young's modulus, surface tension, viscosity, specific heat and others.

Are experiment questions asked in JEE Main?

Yes. Usually 1–2 questions on readings, errors, least count or the graph from an experiment.