CBSE Class 10 Science 2019 · Paper 31/5/3 · Question 4

Principle: an electric motor works on the principle that a current-carrying conductor (its coil) placed in a magnetic field experiences a force. The forces on the two opposite sides of the coil act in opposite directions and make it rotate, converting electrical energy into mechanical energy. Rule: Fleming's left-hand rule. Stretch the thumb, forefinger and middle finger of the left hand so that they are mutually perpendicular. If the forefinger points in the direction of the magnetic field and the middle finger in the direction of the current, then the thumb points in the direction of the force (motion) on the conductor.