Physics · Units And Measurements · NEET
It depends on where the zero sits. Zeros between non-zero digits (like the 0 in 205) always count. Zeros at the front (like in 0.0025) never count, they only fix the decimal place. Zeros at the end count only if there is a decimal point: 2.50 has 3 significant figures, but 250 without a dot is ambiguous.
Just 1. The three zeros are all leading zeros. They only tell you where the decimal point is, so they are not significant. Only the digit 5 is significant. Writing it as 5 x 10^-3 makes this clear: one significant figure.
Without a decimal point, 100 is ambiguous, and by the plain rule it has only 1 significant figure (trailing zeros with no dot are not counted). If you mean 3 significant figures, write 1.00 x 10^2. If you mean 2, write 1.0 x 10^2. This is exactly why scientific notation is used.
Only when a decimal point is shown. In 4.700 the two trailing zeros are significant, so it has 4 significant figures. In 4700 (no dot) the trailing zeros are not counted, so it has 2 significant figures. The decimal point is the signal.
Ignore the power of ten completely. Only count the digits in the number part (the mantissa). For 6.02 x 10^23, count 6, 0 and 2, which is 3 significant figures. This is the safest way to write a value, because there are no ambiguous zeros.
No, exact numbers have unlimited significant figures. If you count 5 apples or use a formula constant like 2 in 2 pi r, that number is exact and never limits your answer. Significant figure rules only apply to measured quantities that carry uncertainty.
Each side of a metallic cube of mass 5.580 kg is measured to be 9.0 cm. Keeping significant figures in view, the density can be best expressed as X x 10^3 kg m^-3. Find X.
The area of a rectangular field of length 55.3 m and breadth 25 m, after rounding off to correct significant figures, is:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Significant figures are all the digits in a measurement that are known reliably, plus the first digit that is uncertain. NCERT gives the example: a pendulum period of 1.62 s has 3 significant figures, where 1 and 6 are certain and 2 is uncertain.
Four. The digits 2, 8, 7 are certain and 5 is the uncertain digit. All four are counted because they are non-zero measured digits, following the NCERT example.
Units and Measurements is a scoring chapter, and NEET regularly asks 1 direct question where you compute a result (area, density, mean) and must report it to correct significant figures. Getting the digit count wrong gives a wrong option even if the arithmetic is right.
No. Converting 5.680 cm to 0.05680 m keeps 4 significant figures. The leading zeros added during conversion are not significant, so the count stays the same. This is a common trick in NEET questions.
Write the number in scientific notation, like a x 10^b. Then simply count the digits in the number part a. All ambiguous trailing and leading zeros disappear, so counting becomes error-free.
