Physics · Units And Measurements · NEET
No. Accuracy is about closeness to the TRUE (correct) value. Precision is about how close your repeated readings are to EACH OTHER. A dartboard helps: accurate = darts near the bullseye; precise = darts tightly grouped (even if the group is far from the bullseye). You can have one without the other.
Yes, this is the most important idea for NEET. Suppose the true length is 20.00 cm but a ruler has a zero error. You measure 20.52, 20.51, 20.53 cm. These are very close to each other, so they are PRECISE. But they are all far from 20.00 cm, so they are NOT accurate. A steady systematic error (like zero error) hurts accuracy while precision can still look good.
No. More decimal places means higher PRECISION (a finer instrument with smaller least count), not higher accuracy. A screw gauge reading 2.53 mm is more precise than a scale reading 3 mm, but if the screw gauge has a zero error, the finer reading can still be less accurate. Precision comes from resolution; accuracy comes from being close to the true value.
The smaller the least count of an instrument, the higher its precision. A metre scale (least count 1 mm) is less precise than a vernier caliper (0.01 cm = 0.1 mm), which is less precise than a screw gauge (0.001 cm = 0.01 mm). Least count sets the smallest change the instrument can resolve, so it directly limits precision. It does not by itself guarantee accuracy.
Systematic errors (zero error, faulty instrument, wrong technique) push all readings in the same direction and reduce ACCURACY. Random errors (small unpredictable fluctuations) scatter readings around a value and reduce PRECISION. You improve accuracy by correcting the systematic cause (calibration, index correction) and improve precision by taking many readings and averaging, or by using a finer instrument.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Accuracy is closeness to the true value; precision is closeness of repeated readings to one another.
You want both. But remember for concept questions: reducing systematic error improves accuracy, while taking more readings or using a finer instrument improves precision.
Averaging mainly improves precision by cancelling random errors. It does not remove a systematic error, so it cannot fix accuracy if a zero error is present.
No. A digital display gives high precision (many digits) but can still be inaccurate if it is not calibrated or has an offset. Digits on screen do not prove closeness to the true value.
