Question

What is the ratio of the specific charge (e/m) of a proton to that of an $\alpha -$particle ?

• A. $1:5$
• B. $1:2$
• C. $1:1/4$
• D. $2:1$

Answer 1

The correct option is D $2:1$

Specific charge $=\frac{e}{m}$
$\alpha$-particle has charge twice of proton charge and 4 times mass of proton mass.
So, $\frac{e}{m}for\alpha -particle=\frac{2q_p}{4q_m}$$=\frac{1}{2}\left(specificchargeofproton\right)$

$\Rightarrow \frac{specificchargeofproton}{specificchargeof\alpha -particle}=\frac{2}{1}$