Question

Electrons enter a uniform magnetic field of intensity $150\times {10}^{-4}T$, perpendicular to it with a velocity of $1.76\times {10}^{8}m/s$. Then the radius of the circular path in which they travel is :
(given e/m of electron$=1.76\times {10}^{11}C/kg).$

• A. $0.0033m$
• B. $0.066m$
• C. $0.0044m$
• D. $0.0055m$

Answer 1

The correct option is B $0.066m$

Radius in a magnetic field
$\Rightarrow radius=\frac{mV}{Bq}=\left(\frac{m}{e}\right)\frac{V}{B}=\left(\frac{{10}^{-11}}{1.76}\right)\left(\frac{1.76\times {10}^8}{150\times {10}^{-4}}\right)m$
$\Rightarrow r=0.0666m$