A beam of cathode rays moves from left to right in a plane of the paper and it enters into a uniform magnetic field acting perpendicular to the plane of the paper and inwards. Now, the cathode rays are deflected :

Downwards

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Upwards

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In a direction perpendicular to the plane of the paper and inwards

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In a direction perpendicular to the plane of the paper and outwards

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Solution

The correct option is A Downwards
The force acting on charges moving with velocity $\to v$ and magnetic field $\to B$ is given as: $\to F = q (\to v \times \to B)$
The direction of $\to v \times \to B$ is upwards for the given velocity and magnetic field. But since the electrons are negatively charged, the direction of force is opposite to that of $\to v \times \to B$ , which is downwards.

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