Physics · Units And Measurements · NEET
The main ones for NEET are: giga (G) = 10^9, mega (M) = 10^6, kilo (k) = 10^3, then the base unit = 10^0, then milli (m) = 10^-3, micro (u) = 10^-6, nano (n) = 10^-9, pico (p) = 10^-12. Notice that each big step from kilo up, and each small step from milli down, changes the power of ten by 3. Also centi (c) = 10^-2 and deci (d) = 10^-1 are the odd ones that change by 1.
By SI rule, prefixes for one million (10^6) and above use a CAPITAL letter (M, G, T), while prefixes below that use a small letter (k, m, u, n, p). So kilo is small k, but mega is capital M. This is why a capital K is wrong for kilo. The one common trap: capital K is reserved for kelvin, the unit of temperature, so writing 5 Kg is technically wrong; it should be 5 kg.
Replace the prefix with its power of ten. nano (n) = 10^-9, so 500 nm = 500 x 10^-9 m = 5 x 10^-7 m. Rule: to change a prefixed value to the base unit, just multiply by the power of ten that the prefix means. This is why the wavelength of light, about 500 nm, is 5 x 10^-7 m.
milli (small m) = 10^-3 (one thousandth, a SMALL number). The one that means 10^3 is kilo (k). An easy check: 1 mm is smaller than 1 m, so milli must make the unit smaller, meaning a negative power. 1 km is bigger than 1 m, so kilo makes it bigger, a positive power.
micro (u) = 10^-6 and nano (n) = 10^-9. Nano is 1000 times smaller than micro because -9 is three powers below -6. So 1 micrometre = 1000 nanometres. In NEET, red blood cells are about 7 um wide, while an atom is about 0.1 nm wide.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Focus on giga (10^9), mega (10^6), kilo (10^3), deci (10^-1), centi (10^-2), milli (10^-3), micro (10^-6), nano (10^-9) and pico (10^-12). These cover almost every value used in NEET numericals.
Physics deals with sizes from atoms (10^-10 m) to galaxies (10^21 m). Prefixes and powers of ten let us write and compare these huge and tiny numbers in a short, clear way, which reduces mistakes in NEET calculations.
Both show powers of ten. A prefix hides the power inside a word attached to the unit (like nm), while scientific notation writes the power openly (5 x 10^-7 m). For NEET you convert prefixes into scientific notation before doing maths.
No. Most prefixes change the power of ten in steps of 3 (kilo, mega, giga; milli, micro, nano). But deci (10^-1) and centi (10^-2) change by 1, so they are exceptions you should memorise separately.
tera (T) = 10^12 for large values, and its opposite pico (p) = 10^-12 for tiny values. These appear less often but can show up in unit conversion questions.
