Question

A charged particle is whirled anticlockwise in a horizontal circle on a frictionless table by attaching it to a string fixed at one point. What will happen to the tension in the string, if a magnetic field is switched on in the vertical direction?

Answer 1

The tension in the string may increase or decrease, the direction of magnetic field is not defined. There will be a Lorentz force on the charged particle which will be perpendicular to both magnetic field and tangential velocity of charge. The direction of force can be found using right-hand thumb rule. Point the first finger in the direction of tangential velocity, second finger along the magnetic field, the thumb will point in the direction of the force.