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Module- II, Lecture-1 D.C.Machines: A machine which works on direct current is defined as a D.C.Machine. D.C.Machines are of two types. (i) D.C.Generator and (ii) D.C.Motor. Sl.No. D.C. Generator 1 2 Definition: Definition: A generator is a rotating machine which converts mechanical energy into electrical energy A motor is a machine which converts electrical energy into mechanical energy Principle: Principle: Whenever a coil is rotated in a magnetic field an e.m.f. will be induced in this coil Whenever a current coil is placed under a magnetic field the coil experiences a mechanical force, and is given by F= BIlSinθ Newtons/coil side. and is given by e=BlvSinθ volts/coil side where, B=The flux density in Tesla, l=the active length of the coil side in meters, v=the velocity with which the coil is moved in meters/sec and θ is the angle between the direction of the flux and the direction of rotation of the coil side. 3 D.C.Motor The direction of the emf induced is fixed by applying the Fleming‟s right hand rule Where, I is the current through the coil in ampere. The direction of the force acting is fixed by applying the Fleming‟s left hand rule. Types and constructional features Salient parts of a D.C.machine are: Field system (poles) Coil arrangement (armature) Commutator Brushes Yoke