Question

An electron $(mass=9\times {10}^{-31}kg,charge=1.6\times {10}^{-19}C)$ moving with a velocity of ${10}^6$m/s enters a magnetic field. If it describes a circle of radius 0.1, then strength of magnetic field must be

• A. $4.5\times {10}^{-5}T$
• B. $1.4\times {10}^{-5}T$
• C. $5.5\times {10}^{-5}T$
• D. $2.6\times {10}^{-5}T$

Answer 1

The correct option is C $5.5\times {10}^{-5}T$

$Bqv=\frac{m{v}^2}{r}$ or

$B=\frac{mv}{rq}$
$=\frac{(9\times {10}^{-31})\times {10}^6}{0.1\times (1.6\times {10}^{-19})}$

$=5.5\times {10}^{-5}T$