Question

A positively charged particle moving due east enters a region of uniform magnetic field directed vertically upwards. The particle will_______.

• A. get deflected in vertically upward direction.
• B. get deflected in opposite direction.
• C. get deflected in downward direction only.
• D. move in a circular path.

Answer 1

The correct option is D move in a circular path.

Using Fleming's left-hand rule we can point the direction of the magnetic field as coming out of the paper (shown as dots).
The positive charge is entering the field and is moving perpendicular to the field. Here:
-Index finger $\to$ point upwards vertically in the direction of the field,
-Middle finger $\to$ points in the direction of the current towards east.
-Thumb $\to$ gives us the direction of the force which is perpendicular to both current and magnetic field towards north.

This propels the charge to move in the direction of the force.
But we observe that the Fleming's left-hand rule can be applied again in its new position- B and then we observe the particle moves towards C.
Basically, the particle in the field continues this path which is a circular path till the field is present.