Electric Field And Field Lines

Electric field is defined as the force experienced per unit positive charge, expressed as $E=\frac{F}{q}$, a relation emphasised in NCERT Class 12, Chapter 1 (Electric Charges and Fields). The droplet carries $q=5\times 10^{-9}$ C and feels a force $F=2\times 10^{-3}$ N. Dividing gives $E=\frac{2\times 10^{-3}}{5\times 10^{-9}}$. Working the powers of ten, $\frac{2}{5}=0.4$ and $\frac{10^{-3}}{10^{-9}}=10^6$, so $E=0.4\times 10^6=4\times 10^5$ N/C. The value $2.5\times 10^5$ N/C is wrong because it inverts the ratio, dividing charge by force. The value $1\times 10^6$ N/C is wrong because it rounds $0.4$ up to $1$ without justification. The value $1\times 10^4$ N/C is wrong because it mishandles the exponent difference by two orders. This laboratory setup echoes Millikan's oil-drop experiment where droplets are balanced in fields. A magnitude check confirms nano-coulomb charges in milli-newton forces need fields of order $10^5$ N/C, matching the answer's exponent and sign.