Question

The charge to mass ratio of $\alpha -particle$ is approximately ____ of the charge to mass ratio of a proton is:

• A. half
• B. twice
• C. 4 times
• D. 6 times

Answer 1

The correct option is B twice

Alpha particle is a helium nucleus containing two protons and two neutrons so its charge is $twice$ the proton’s charge while the mass is about 4 times greater.

Let the charge of the proton be $+e$, then the charge of the alpha particle will be $+2e$. Similarly mass of the proton be m, then the mass of the alpha particle will be $4m$.

Specific charge = charge/mass of the substance.

For proton, specific charge =$\frac{e}{m}$

For alpha particle, specific charge = $\frac{2e}{4m}$

Therefore the ratio is = $\frac{e}{m}$ x $\frac{4m}{2e}=2:1$

Hence, the charge to mass ratio of an alpha particle is approximate twice the charge to mass ratio of a proton.

So, the correct option is $B$