Question

An electron (mass $=9\times {10}^{-31}kg$. Charge $=1.6\times {10}^{-19}C$) whose kinetic energy is $7.2\times {10}^{-18}$ joule is moving in a circular orbit in a magnetic field of $9\times {10}^{-5}$ weber $/m$. The radius of the orbit is

• A. $1.25cm$
• B. $2.5cm$
• C. $12.5cm$
• D. $25.0cm$

Answer 1

Answer: (D)

$25.0cm$

$r=\frac{\sqrt{2mE}}{qB}=\frac{\sqrt{2\times 9\times {10}^{-31}\times 7.2\times {10}^{-18}}}{1.6\times {10}^{-19}\times 9\times {10}^{-5}}$
$=0.25m=25cm$