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4.Moving Charges and Magnetism
medium
An electron (mass $= 9 \times 10^{-31}\,kg$. Charge $= 1.6 \times 10^{-19}\,C$) whose kinetic energy is $7.2 \times 10^{-18}$ $joule$ is moving in a circular orbit in a magnetic field of $9 \times 10^{-5} \,weber/m^2$. The radius of the orbit is.....$cm$
A
$1.25$
B
$2.5$
C
$12.5 $
D
$25$
Solution
(d) $r = \frac{{\sqrt {2mE} }}{{qB}} = \frac{{\sqrt {2 \times 9 \times {{10}^{ – 31}} \times 7.2 \times {{10}^{ – 18}}} }}{{1.6 \times {{10}^{ – 19}} \times 9 \times {{10}^{ – 5}}}}$
= $0.25\, m = 25\, cm$
Standard 12
Physics