Question: Q. 9. (i) Draw a labelled diagram of an $a c$ generator and state its working principle. $\mathrm{R}$ [Delhi I, II, III 2014]
(ii) How is magnetic flux linked with the armature coil changed in a generator ?
(iii) Derive the expression for maximum value of the induced emf and state the rule that gives the direction of the induced emf.
(iv) Show the variation of the emf generated versus time as the armature is rotated with respect to the direction of the magnetic field.
U] [Delhi Comptt. I, II, III 2014,
O.D. Comptt. I, II, III 2012]
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Solution:
Ans. (i) Try yourself, Labelled Diagram: Refer to Q. 3 (a), Long Answer Type Questions.
Principle :
It works on the principle of electromagnetic induction, i.e., when a coil continuously rotates in a magnetic field, the magnetic flux associated with it keeps on changing; thus an emf is induced in it.
(ii) When the coil rotates in a magnetic field, its effective area, i.e., $A \cos \theta$, (i.e., area normal to the magnetic field) keeps on changing. Hence magnetic flux $\phi=N B A \cos \theta$, keeps on changing.
(iii) Try yourself, Expression : Refer to Q. 3(a), Long Answer Type Questions.
[CBSE Marking Scheme, 2014] 1
