A positive charge is moving towards south in a space where magnetic fi

A positive charge is moving towards south in a space where magnetic field is pointing in the north direction. The moving charge will experience :

a deflecting force towards north direction.

a deflecting force towards east direction.

a deflecting force towards west direction.

no deflecting force.

Answer is Right!

Answer is Wrong!

This question was previously asked in

UPSC NDA-1 – 2023

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The force experienced by a positive charge (q > 0) moving with velocity $\vec{v}$ in a magnetic field $\vec{B}$ is given by the Lorentz force formula: $\vec{F} = q (\vec{v} \times \vec{B})$.

The direction of the velocity $\vec{v}$ is towards south, and the direction of the magnetic field $\vec{B}$ is towards north. These two directions are opposite to each other. The angle between $\vec{v}$ and $\vec{B}$ is 180 degrees.

The magnitude of the cross product $\vec{v} \times \vec{B}$ is $|\vec{v}| |\vec{B}| \sin(\theta)$, where $\theta$ is the angle between $\vec{v}$ and $\vec{B}$. Since $\theta = 180^{\circ}$, $\sin(180^{\circ}) = 0$. Therefore, the magnitude of the force $|\vec{F}| = q |\vec{v}| |\vec{B}| \sin(180^{\circ}) = 0$. The moving charge will experience no deflecting force.

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