Practical Physics / Laboratory Skills
What this domain tests
Practical Physics assesses instrument handling, least count, zero error, measurement tables, graph plotting and error analysis in the First Year laboratory.
Core rules
- Vernier caliper: least count = 1 MSD − 1 VSD, commonly 0.1 mm; reading = MSR + (VSD × LC) − zero error.
- Screw gauge: pitch = distance moved per full rotation, commonly 0.5 mm; LC = pitch/50 = 0.01 mm; reading = MSR + (circular scale × LC) − zero error.
- Simple pendulum: measure L from the point of suspension to the centre of the bob; time 20 oscillations and divide by 20.
- Sonometer and resonance column: use the mean of repeated readings and correct for end correction where required.
- Plot graphs with labelled axes, units and a best-fit straight line; calculate slope from widely separated points.
Worked example
A screw gauge has pitch 0.5 mm and 50 circular divisions, so LC = 0.01 mm. Main scale reads 2 mm and the circular scale reads 45. Reading = 2 + 45 × 0.01 = 2.45 mm. If the zero error is −0.02 mm, the corrected value is 2.45 − (−0.02) = 2.47 mm. A negative zero error is added, not subtracted.
Traps
Reading the main scale beyond the zero of the vernier; applying zero error with the wrong sign; measuring pendulum length to the top of the bob; parallax error when reading a meniscus or scale; plotting raw readings without converting units; using a single reading instead of a mean.