Generation of a Sinusoidal Waveform

In our tutorials about Electromagnetism, we saw how an electric current flowing through a conductor can be used to generate a magnetic field around itself, and also if a single wire conductor is moved or rotated within a stationary magnetic field, an "EMF", (Electro-Motive Force) will be induced within the conductor due to this movement. From this tutorial we learnt that a relationship exists between Electricity and Magnetism giving us, as Michael Faraday discovered the effect of "Electromagnetic Induction" and it is this basic principal that is used to generate a Sinusoidal Waveform.

In the Electromagnetic Induction, tutorial we said that when a single wire conductor moves through a permanent magnetic field thereby cutting its lines of flux, an EMF is induced in it. However, if the conductor moves in parallel with the magnetic field in the case of points A and B, no lines of flux are cut and no EMF is induced into the conductor, but if the conductor moves at right angles to the magnetic field as in the case of points C and D, the maximum amount of magnetic flux is cut producing the maximum amount of induced EMF. Also, as the conductor cuts the magnetic field at different angles between points A and C, 0 and 90^o the amount of induced EMF will lie somewhere between this zero and maximum value. Then the amount of emf induced within a conductor depends on the angle between the conductor and the magnetic flux as well as the strength of the magnetic field.

An AC generator uses the principal of Faraday's electromagnetic induction to convert a mechanical energy such as rotation, into electrical energy, a Sinusoidal Waveform. A simple generator consists of a pair of permanent magnets producing a fixed magnetic field between a north and a south pole. Inside this magnetic field is a single rectangular loop of wire that can be rotated around a fixed axis allowing it to cut the magnetic flux at various angles as shown below.

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CBSE TEST PAPER-01

CLASS - XII PHYSICS (Electromagnetic Induction and Alternating current)

1. A metallic wire coil is stationary in a non – uniform magnetic field. What is the

emf. Induced in the coil?

[1]

2. Why does metallic piece becomes very hot when it is surrounded by a coil

carrying high frequency (H.F) alternating current?

[1]

3. IF the rate of change of current of 2A/s induces an emf of 1omV in a solenoid.

What is the self inductance of the solenoid?

[1]

4. A circular copper disc. 10 cm in radius rotates at a speed of 2

axis through its centre and perpendicular to the disc. A uniform magnetic field

of 0.2T acts perpendicular to the disc.

1) Calculate the potential difference developed between the axis of the disc

and the rim.

2) What is the induced current if the resistant of the disc is 2

[3]

5. How is the mutual inductance of a pair of coils affected when

(1) Separation between the coils is increased.

(2) The number of turns of each coil is increased.

(3) A thin iron sheet is placed between two coils, other factors remaining the

same. Explain answer in each case.

[3]

6. Distinguish between resistances, reactance and impedance of an a.c. circuit? [3]

7. A sinusoidal voltage V = 200 sin 314t is applied to a resistor of 10

p rad/s about anW?W

resistance. Calculate

(1) rms value of the voltage

(2) rms value of the current

(3) Power dissipated as heat in watt.

[3]

8. (a) State the condition under which the phenomenon of resonance occurs

in a series LCR circuit. Plot a graph showing the variation of current

with frequency of a.c. sources in a series LCR circuit.

(b) Show that in a series LCR circuit connected to an a.c. source exhibits

resonance at its natural frequency equal to

1/(LC)?

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CBSE TEST PAPER-01

CLASS - XI PHYSICS (Kinematics)

Topic: - Motion in Straight Line

1. Under what condition is the relation

2. Two balls of different masses are thrown vertically upward with same initial speed.

Which one will rise to a greater height?

[1]

3. What is the relative velocity of two bodies having equal velocities? [1]

4. Write the characteristics of displacement? [2]

5. Draw displacement time graph for uniformly accelerated motion. What is its

shape?

[2]

6. Sameer went on his bike from Delhi to Gurgaon at a speed of 60km/hr and came

back at a speed of 40km/hr. what is his average speed for entire journey.

[2]

7. Define

8. A particle is moving along a straight line and its position is given by the relation

s =ut correct? [1]J = v + at from velocity time graph. [3]

x

= (t3 - 6t 2 -15t + 40)m

Find (a) The time at which velocity is zero.

(b) Position and displacement of the particle at that point.

(c) Acceleration for the particle at that line.

[3]

9. Velocity time graph of a moving particle is shown. Find the displacement (1) 0 – 4 s

(2) 0 – 8 (3) 0 12 s from the graph. Also write the differences between distance and

displacement.