Question

An electron enters a magnetic field of $0.01T$ with a velocity of ${10}^7$ m/s, describing a circular path of radius $0.6cm$. Then the value of $e/m$ of electron is :

• A. $1.76\times {10}^{11}C/kg$
• B. $2.04\times {10}^{11}C/kg$
• C. $1.72\times {10}^{11}C/kg$
• D. $1.66\times {10}^{11}C/kg$

Answer 1

The correct option is D $1.66\times {10}^{11}C/kg$

Radius in a magnetic field $=\frac{mV}{eB}$
$\Rightarrow \frac{e}{m}=\frac{V}{Br}=\frac{{10}^7\times {10}^2}{0.01\times 0.6}$

$\Rightarrow \frac{e}{m}=1.666\times {10}^{11}C/kg$