when to use flemings left hand rule and when to use fleming right hand rule?
As answered previously...
According to Fleming's left-hand rule:Hold the forefinger,the center finger and the thumb of left hand at right angles to one another. Adjust fingers in such a way that the forefinger points in the direction of magnetic field and center finger points in the direction of current,then the direction in which the thumb points,gives the direction of force acting on the conductor.
According to Fleming's right hand rule:Hold the thumb,the forefinger and the center finger of right hand at right angles to one another. Adjust fingers in such a way that forefinger points in the direction of magnetic field,the thumb points in the direction of motion of conductor,then the direction in which center finger points,gives the direction of induced current in the conductor.
From the above we see that the left hand rule determines the direction of force acting on a current carrying wire placed in a magnetic field,whereas right hand rule gives the direction of induced current produced in a straight conductor moving in a magnetic field.