Chemistry · Some Basic Concepts Of Chemistry · NEET
Precision looks only at your OWN readings and asks: are they close to each other? Accuracy compares your reading to the TRUE value and asks: is it correct? So precision is about consistency (repeatability), and accuracy is about correctness. You need the true value to judge accuracy, but not to judge precision.
Yes. This is the most tested idea. In the NCERT example the true value is 2.00 g. Student A gets 1.95 g and 1.93 g. These two are very close to each other (so PRECISE), but both are far from 2.00 g (so NOT accurate). This usually happens when an instrument has a fixed error, like a balance that always reads a bit low.
It can happen by luck. If your readings are far apart (say 1.80 g and 2.20 g) but their average lands near the true 2.00 g, the average looks accurate even though the readings are not precise. Because it depends on averaging out big scatter, we do not trust it. Good science wants readings that are BOTH precise and accurate.
Student C. Student C reports 2.01 g and 1.99 g. These two are close to each other (precise) AND both are very close to the true value 2.00 g (accurate). Student A is precise but not accurate. Student B (1.94 g and 2.05 g) is neither precise nor accurate because the readings are far apart and far from 2.00 g.
No. To check precision you only compare your readings with each other, so you do not need to know the correct answer. To check accuracy you MUST know the true value, because accuracy is the agreement of your value with the true value. This is a common trap in one-line NEET questions.
Use the dartboard picture. Accuracy = darts near the bulls-eye (true value). Precision = darts grouped tightly together, wherever they land. If they are tight but off-center: precise, not accurate. If they are near center and tight: both. Say the hook: 'Accuracy Aims at truth, Precision Packs together.'
Try the real previous-year questions from this chapter — each with the answer and a full solution.
For NEET you must know BOTH definitions and be able to classify readings as precise, accurate, both, or neither. The most asked point is that a reading can be precise but not accurate. Learn the NCERT 2.00 g example by heart.
Precision: closeness of repeated readings to each other. Accuracy: agreement of a reading with the true value. These are the exact NCERT wordings, so use them in answers.
Every experiment gives measurements, and you must judge if your data is reliable. Understanding precision and accuracy helps you know when readings are trustworthy and when your instrument or method has an error. It also links directly to significant figures and uncertainty in measurement.
The next idea is uncertainty in measurement, which uses significant figures and scientific notation to show how sure we are about a value. Precision and accuracy set up why we need to report uncertainty at all.
