Question

A proton with kinetic energy K describes a circle of radius r in a uniform magnetic. An $\alpha$- particle with kinetic energy K moving in the same magnetic field will describe a circle of radius?

• A. $\frac{r}{2}$
• B. r
• C. $2r$
• D. $4r$

Answer 1

The correct option is C $2r$

WE KNOW THAT

charge on proton = q

charge on alpha particle = 2q

mass of proton =m

mass of alpha particle =4m

for proton

$r=\frac{m\times v}{q\times B}$

for alpha particle

$R=\frac{4m\times v}{2q\times B}$

$R=\frac{2m\times v}{q\times B}$

$R=2r$