CBSE Class 10 Science 2018 · Paper 31/1 · Question 21

(a) 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) acting on the conductor. (b) Principle: an electric motor works on the principle that a current-carrying coil (conductor) placed in a magnetic field experiences a force. The forces on the two arms of the coil are in opposite directions, so the coil rotates, converting electrical energy into mechanical energy. (c) (i) Armature: the coil wound on a soft iron core; it carries the current and rotates in the magnetic field, turning the axle, and the soft iron core enhances the power of the motor. (ii) Brushes: they press against the split ring and allow easy transfer of current between the external circuit (battery) and the rotating coil. (iii) Split ring: it reverses the direction of the current in the coil after every half rotation, so that the coil keeps rotating continuously in the same direction.