This rule is used for the determining the direction of magnetic field. If we rotate screw in the cork by a screwdriver. The current direction is same as the direction of screw advances, and the direction of rotation of the screw will determine the direction of the magnetic field.
Hold the tomb, fore finger and middle finger of the right hand in such away that they make 900 with other. If tomb points the direction of the motion of the conductor, fore finger points the direction of the magnetic field then the middle finger will points to the direction of induced emf (voltage).
Hold the tomb, fore and middle finger of the left hand in such a way that they make 90° with other. The forefinger indicates the direction of the field, middle
Indicates the direction of current, and then the tomb will indicate the direction of the motion of the conductor. This is called m/r rule.
Whenever a current carrying conductor is placed in a magnetic field, it Experiences a mechanical force. This force is directly proportional to the current flowing, I in the conductor in ampere and it is also directly proportional to the length of the conductor, L in meter and magnetic flux density, B in Weber/m- of the magnetic field. Hence we can write
To compare the above factor we can write
F BIL Newton