Question

Explain right-hand thumb rule and left-hand thumb rule.

Answer 1

Whenever a current carrying conductor comes under a magnetic field, there will be a force acting on the conductor and on the other hand, if a conductor is forcefully brought to a magnetic field, there will be an induced current in that conductor. In both of the phenomenon, there is a relation between magnetic field, current and force. This relation is directionally determined by Fleming Left-Hand rule and Fleming Right-Hand rule respectively.
'Directionally' means these rules do not show the magnitude but show the direction of any of the three parameters (magnetic field, current, force) if the direction of other two is known. Fleming Left-Hand rule is mainly applicable for electric motor and Fleming Right-Hand rule is mainly applicable for an electric generator. In late 19th century, John Ambrose Fleming introduced both these rules and as per his name, the rules are well known as Fleming left and right-hand rule.
Fleming Right Hand Rule

As per Faraday's law of electromagnetic induction, whenever a conductor moves inside a magnetic field, there will be an induced current in it. If this conductor gets forcefully moved inside the magnetic field, there will be a relation between the direction of applied force, magnetic field and the current. This relation among these three directions is determined by Fleming Right-Hand rule
This rule states "Hold out the right hand with the first finger, second finger and thumb at right angles to each other. If forefinger represents the direction of the line of force, the thumb points in the direction of motion or applied force, then second finger points in the direction of the induced current.

Fleming's left-hand rule is applied when a current carrying conductor is placed in a magnetic field. In order to find the direction of force experienced by the current carrying conductor, one should align the first finger with the direction of magnetic field, the mid-finger with the direction of current and the thumb perpendicular to both as shown in the figure below. The thumb in this situation will give the direction of magnetic force.