Question

An electron is moving with velocity ${10}^{7}m/s$ on a circular path of radius 0.57 cm in a magnetic field of ${10}^{-2}wb/m^2$. The value of e/m for electron will be:

• A. $1\cdot 76\times {10}^{9}C/kg$
• B. $1\cdot 76\times {10}^{10}C/kg$
• C. $1\cdot 76\times {10}^{11}C/kg$
• D. $1\cdot 76\times {10}^{12}C/kg$

Answer 1

The correct option is C $1\cdot 76\times {10}^{11}C/kg$

We know, $evB=\frac{m{v}^2}{r}$
$\Rightarrow \frac{e}{m}=\frac{v}{Br}=\frac{{10}^7}{{10}^{-2}\times 0.0057}$
$=1.76\times {10}^{11}C/kg$