Read a vernier callipers and a screw gauge
"Read a vernier callipers and a screw gauge" is a free, interactive Class 11 Physics simulation for NEET and JEE, built on the NCERT section "Uncertainty in calculated results" in Units and Measurements. A vernier calliper and a screw gauge gripping a rod: main-scale reading + coinciding division × least count, with optional zero error, gives the true reading. NEET has asked about this idea 5 times in 10 years of papers. JEE Main asked 61 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).
From the lesson Uncertainty in calculated results in Units and Measurements. Change the values and watch what happens.
What it shows
NCERT §1.3.3
A vernier calliper and a screw gauge gripping a rod: main-scale reading + coinciding division × least count, with optional zero error, gives the true reading.
Controls
5 to try
- Togglevernier calliper / screw gauge
- Dragjaw or thimble to close on the object
- Slidervernier divisions 10–50 (or screw pitch 0.5–1 mm, 50–100 circular divisions)
- Togglezero error none / positive / negative
- Readoutleast count, observed and corrected reading
Try this
With a +0.03 cm zero error on the calliper, read the rod's diameter and enter the corrected value to 0.01 cm (checked against the hidden true size).
Common mistake
Adding a positive zero error instead of subtracting it, and taking least count as one main-scale division.
In NEET
10 years of papers
Asked 5 times in 10 years of NEET.
See the past questions: Units and Dimensions, Units and Measurements (chapter)
In JEE Main
42 shifts analysed
61 questions from Units and Measurements across the 42 JEE Main shifts Lumi has analysed (2017–2026).
The idea behind it
NCERT §1.3.3
- A reading from an instrument carries an uncertainty of about its least count: a length of 16.2 cm read on a metre scale is 16.2 ± 0.1 cm.
- The relative (percentage) error is the uncertainty divided by the value: ±0.1 cm on 16.2 cm is about ±0.6%, and ±0.1 cm on 10.1 cm is about ±1%.
- When measured values are multiplied or divided, their percentage errors add: the area l × b = 163.62 cm² carries ±1.6%, about ±2.6 cm², so it is quoted as 164 ± 3 cm².
- The same absolute uncertainty is a larger relative error on a smaller value: ±0.01 g is ±1% of 1.02 g but only ±0.1% of 9.89 g.
- Uncertainties in a sum or difference follow decimal places, not significant figures, so a difference can lose figures: 12.9 g − 7.06 g is 5.8 g, not 5.84 g.
- If the data are good to n significant figures, a result obtained by combining them is valid to about n significant figures, fewer if data are subtracted.
Questions
5 answers
- What does the "Read a vernier callipers and a screw gauge" simulation show?
- A vernier calliper and a screw gauge gripping a rod: main-scale reading + coinciding division × least count, with optional zero error, gives the true reading.
- What mistake does the "Read a vernier callipers and a screw gauge" simulation fix?
- A common mistake it clears up: adding a positive zero error instead of subtracting it, and taking least count as one main-scale division.
- Has NEET asked about this idea?
- Yes. NEET has asked about this idea 5 times in 10 years of papers.
- Does JEE Main ask questions from Units and Measurements?
- Yes. JEE Main asked 61 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).
- Is this simulation free?
- Yes. It is free and runs in the browser on a phone or a laptop. It belongs to the lesson "Uncertainty in calculated results" in Units and Measurements (Class 11 Physics).
Embed this simulation
Free, with a link back
Teaching this idea? Put the simulation on your own page or LMS with this code.