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Draw a labelled schematic diagram of an a.c. generator. Explain briefly its principle and working. |
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Answer» Solution :The labelled diagram of an a.c. generator is given in Fig. 6.55. Principle: Ana.c. generator is based on the phenomenon of electromagnetic induction. If a rectangular armature coil rotates about its axis in a uniform magnetic field, the magnetic flux linked with the coil changes and an induced emf is set up in the coil. The direction of induced current is given by Fleming.s right hand rule. WORKING : When an armature coil of N turns and each turn enclosing area A is placed in a uniform magnetic field of strength B making an angle `theta` from normal to the direction of magnetic field, magnetic flux linked with the coil is `phi = N B Acostheta.` As the coil is rotated about its own axis with an angular speed `omega` then value of angle `theta = omegat` and hence, magnetic flux changes and an induced emf is developed across the ends of coil. As `phi = N BA COS omegat` `therefore` Induced emf `varepsilon = -(dphi)/dt =N B Aomegasin omegat = varepsilon_(0) sin omegat` where `varepsilon_(0) = N B A omega = "maximum (PEAK)"` value of induced emf. It is obvious that induced emf is sinusoidal in nature. 
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