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8.Electromagnetic waves
medium
A beam of light travelling along $X$-axis is described by the electric field $E _{ y }=900 \sin \omega( t - x / c )$. The ratio of electric force to magnetic force on a charge $q$ moving along $Y$-axis with a speed of $3 \times 10^{7}\,ms ^{-1}$ will be.
[Given speed of light $=3 \times 10^{8}\,ms ^{-1}$ ]
A
$1: 1$
B
$1: 10$
C
$10: 1$
D
$1: 2$
(JEE MAIN-2022)
Solution
$E _{ y }=900 \sin \left(\omega t -\frac{\omega x }{ c }\right)$
$E _{0}=900$
$F _{ E }= q E _{0}$
$F _{ B }= qvB _{0}$
$\frac{ F _{ E }}{ F _{ B }}=\frac{ E _{0}}{ vB }=\frac{ c }{ v }=\frac{3 \times 10^{8}}{3 \times 10^{7}}=10: 1$
Standard 12
Physics
