Question

An electron enters a magnetic field of intensity ${10}^{-4}Wb/m^2$, with a velocity of $106m/s$ and describes a circular path of radius $5.6cm$. The value of $\frac{e}{m}$ of electron is :

• A. $1.79\times {10}^{7}C/kg$
• B. $1.89\times {10}^{7}C/kg$
• C. $1.69\times {10}^{7}C/kg$
• D. $1.66\times {10}^{7}C/kg$

Answer 1

Answer: (B)

$1.89\times {10}^{7}C/kg$

Radius in Magnetic field $r=\frac{mV}{eB}$
$\Rightarrow \frac{e}{m}=\frac{V}{Br}=\frac{10.6\times {10}^2}{5.6\times {10}^{-4}}$

$\Rightarrow \frac{e}{m}=1.8928\times {10}^{7}C/kg$