Question

A cathode ray beam is bent into an arc of a circle of radius $0.02m$ by a field of magnetic induction $4.55mT$. The velocity of electrons is:
(Given $e=1.6\times {10}^{-19}c$ and $m=9.1\times {10}^{-31}kg$)

• A. $2\times {10}^{7}m/s$
• B. $3\times {10}^{7}m/s$
• C. $1.6\times {10}^{7}m/s$
• D. $3.2\times {10}^{7}m/s$

Answer 1

The correct option is C $1.6\times {10}^{7}m/s$

Radius in Magnetic field $=\frac{mV}{eB}$

$\Rightarrow V=\frac{Ber}{m}$

$\Rightarrow V=\frac{4.55\times {10}^{-3}\times 1.6\times {10}^{-19}\times 0.02}{9.1\times {10}^{-31}}$

$\Rightarrow V=1.6\times {10}^{7}m/s$