Ncert Exercises & Solutions

2.39 In Milikan’s experiment, a static electric charge on the oil drops has been obtained by shining X-rays. If the static electric charge on the oil drop is –1.282 × 10–18C, calculate the number of electrons present on it.

Charge on the oil drop = 1.282 × $10^{- 18}$ C
Charge on one electron = 1.6022 × $10^{- 19}$ C
$∴$ Number of electrons present on the oil drop

$= \frac{1.282 x 10^{- 18} C}{1.6022 x 10^{- 19} C}$
$= 0.8001 x 10^{1}$
$= 8.0$