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  4. A uniform magnetic field B exists along y -axis and a uniform electric field of magnitude 104V/m exists along negative z -axis. If a -16× 10- 18C charge passes through the field along x -axis without any deflection. Magnitude of B is

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Q. A uniform magnetic field $B$ exists along $y$ -axis and a uniform electric field of magnitude $10^{4}V/m$ exists along negative $z$ -axis. If a $-16\times 10^{- 18}C$ charge passes through the field along $x$ -axis without any deflection. Magnitude of $B$ is

NTA AbhyasNTA Abhyas 2020

Solution:

Solution
As per question $\overset{\rightharpoonup}{B}$ is perpendicular to $\overset{\rightharpoonup}{E}$ and charge is moving undeflected, so magnetic force should be equal to electric force, i.e, $qE=qvB$ .
$\Rightarrow E=vB$
$\Rightarrow B=\frac{E}{v}=\frac{10^{4} V/m}{10 m/s}=10^{3}Wb/m^{2}$