CBSE Class 12 Physics Alternating Current Important Questions

CBSE Class 12 Physics Alternating Current Important Questions. Please refer to the examination notes which you can use for preparing and revising for exams. These notes will help you to revise the concepts quickly and get good marks.

Comprehension
The a.c. generator which is one of the most important applications of the phenomenon of electromagnetic induction converts mechanical energy into electrical energy. A rectangular coil consisting of a large number of turns of copper wire would over a soft iron core is rotated between the pole pieces of a permanent strong magnet. The magnetic flux through the coil changes continuously with time, thus producing induced emf given by
E = E₀ sin ωt
When a load resistor R is connected across the terminals, a current I flows through the circuit.
I = E/R =E₀/R sin ωt = I₀ sin ωt

Where I₀ = E₀/R. Such a current is called a.c. or alternating current.

1. In an a.c. generator, a coil of area A and having N turns rotates in a magnetic field B. The magnetic flux through the coil is
(a) maximum equal to NAB when the plane of the coil is perpendicular to the magnetic field.
(b) zero when the plane of the coil is parallel to the field.
(c) 1/2 NAB when the plane of the coil makes an angle of 60° with the field.
(d) 1/4 NAB when the plane of the coil makes an angle of 30° with the field.

2. In an a.c. generator, initially (i.e. at t = 0) the plane of the coil is normal to the magnetic field. Which graph shown in the figure represents the variation of induced emf E with time t ?

3. In an a.c. generator, the peak value of the induced emf depends upon the
(a) frequency of rotation of the coil
(b) area of the coil
(c) number of turns in the coil
(d) strength of the magnetic field

4. In an a.c. generator
(a) the coil is wound over a soft iron core in order to increase the flux.
(b) an electromagnetic field with an alternating current in used.
(c) the output is always taken across a load resistor
(d) the mechanical energy of the rotating coil is converted into electrical energy

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