Question

Compare the specific charge $\left(e/m\right)$ of an electron with that of a hydrogen ion:

• A. $1:1$
• B. $1840:1$
• C. $1:1840$
• D. $2:1$

Answer 1

Answer: (B)

$1840:1$

Mass of proton $=m_p$

Mass of electron $=m_e$ and

Magnitude of charge of electron $=e=$ magnitude of charge of proton

so, for electron, the specific charge $S_1=\frac{e}{m}=\frac{e}{m_e}$ and for proton, the specific charge

$S_2=\frac{e}{m_p}$
The mass of hydrogen ion is 1840 times the mass of electron. $m_p=1840m_e$

The ratio of e/m, (charge/mass) i.e., specific charge for electron and proton

$\frac{S_1}{S_2}=\frac{e/m_e}{\left(e/1840m_e\right)}=1840:1$