What is the value of the specific charge e/m of the electron?

The correct answer is Option (2) → \( 1.76\times10^{11}\,\mathrm{C/kg} \)

The specific charge of the electron is its charge per unit mass, \( e/m \), so it is measured in coulomb per kilogram. Taking \( e=1.602\times10^{-19}\,\mathrm{C} \) and \( m=9.11\times10^{-31}\,\mathrm{kg} \):

    \( \begin{aligned} \frac{e}{m} &= \frac{1.602\times10^{-19}\,\mathrm{C}}{9.11\times10^{-31}\,\mathrm{kg}} \\ &\approx 1.76\times10^{11}\,\mathrm{C/kg} \end{aligned} \)

NCERT (2026-27):
Introduction – “… J. J. Thomson was the first to determine experimentally the speed and the specific charge [charge to mass ratio (e/m)] of the cathode ray particles. They were found to travel with speeds ranging from about 0.1 to 0.2 times the speed of light (3 ×10⁸ m/s). The presently accepted value of e/m is 1.76 × 10¹¹ C/kg.”