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JEE Main 2022 (27 Jul, Shift 1) · Nature of EM Waves & Wave Equation

Nature of EM Waves & Wave Equation question from JEE Main 2022 (27 Jul, Shift 1)

Q39JEE Main 2022 · 27 JUL · SHIFT 1Medium

Nature of EM Waves & Wave Equation

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 $3 \times 10^{7}\text{ ms}^{-1}$ will be:

(Given speed of light $= 3 \times 10^{8}\text{ ms}^{-1}$ )

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Answer: (c)

$F_E = qE$ , $F_B = qvB$ with $B = E/c$ (along $z$ , perpendicular to $\vec v$ ).
$\dfrac{F_E}{F_B} = \dfrac{c}{v} = \dfrac{3\times10^{8}}{3\times10^{7}} = 10$
So the answer is (c) 10 : 1.

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