Physics · Units And Measurements · NEET
Not always. First write the number as a × 10^b with a between 1 and 10. If a is 5 or less, keep b as it is. If a is more than 5, add 1 to b (because you round a up to 10, which is 10^1). Example: 8.4 × 10^3 has a = 8.4 (more than 5), so order of magnitude = 3 + 1 = 4, not 3. But 3.2 × 10^3 has order of magnitude 3.
Step 1: write it in scientific notation a × 10^b. Step 2: look at a. Step 3: if a is 5 or less the order of magnitude is b; if a is more than 5 it is b + 1. Example: 1.28 × 10^7 m (Earth's diameter): a = 1.28 which is 5 or less, so order of magnitude = 7.
Order of magnitude only gives a rough size, in powers of ten. Any a between 1 and 10 is closer either to 1 (which is 10^0) or to 10 (which is 10^1). We pick the nearer one. The cutoff NCERT uses is 5: if a is 5 or less, treat it as 1; if a is more than 5, treat it as 10. This tells you roughly how many times bigger one thing is than another.
Scientific notation is the exact number written as a × 10^b (keeps every significant figure). Order of magnitude throws away the exact value of a and keeps only the power of ten, so it is a rough estimate. Example: 1.06 × 10^-10 m in scientific notation, but order of magnitude -10.
It is -6. The order of magnitude keeps the sign of the exponent. A hydrogen atom of size 1.06 × 10^-10 m has order of magnitude -10 (negative), while Earth's diameter 1.28 × 10^7 m has order of magnitude +7. The difference 7 - (-10) = 17 tells you Earth is 17 orders of magnitude bigger.
Each side of a metallic cube of mass 5.580 kg is measured to be 9.0 cm. Keeping the significant figures in view, the density of the material of the cube can be best expressed as X × 10^3 kg m^-3, where the value of X is:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Writing a number as a × 10^b, where a is between 1 and 10 and b is a whole-number power of ten, for example 4.700 × 10^2 cm.
No. The power of 10 is irrelevant to counting significant figures. Only the digits in a (the base number) are counted. So 4.700 × 10^3 has 4 significant figures, same as 4.700.
Earth's diameter is order of magnitude 7 and a hydrogen atom is order of magnitude -10. The difference is 7 - (-10) = 17, so Earth is 17 orders of magnitude larger.
Yes. NEET often asks answers in the form X × 10^b and mixes it with significant figures and unit conversion. Writing in scientific notation removes ambiguity and is expected in the final answer choices.
Move the decimal to just after the first non-zero digit: 4.5. You moved it 4 places to the right, so the power is -4. Answer: 4.5 × 10^-4 s. Its order of magnitude is -4 (since 4.5 is 5 or less).
