DAY 15 to 18 for FINAL STEP REVISION on EMI and AC ! Requires only 6 Hrs!

Electromagnetic Induction (EMI)-

1. State and Explain Faraday’s laws of electromagnetic induction.
2. State Lenz’ Law and show that it is in accordance with the law of conservation of energy.
3. Use Lenz’ law to find the direction of induced emf in a coil when (a) a north pole is brought towards the coil (b) north pole taken away from the coil (c) A south pole is brought towards the coil and (d) a south pole is taken away from the coil, Draw illustrations in each case.
4. What is motional emf. Deduce an expression for it. State Fleming’s right hand rule to find the direction of induced emf.
5. What are eddy currents? Describe the applications of eddy currents.
6. Explain the working of (a) Electromagnetic Brakes (b) Induction Furnace
7. Which physical quantity is called the INERTIA OF ELECTRICITY? Why is its called so?
8. Define self induction and self inductance. What is its unit? Write its dimensions.
9. Derive an expression for the self inductance of a long solenoid.
10. Explain the phenomenon of mutual induction and define mutual inductance. Write the unit and dimensions of mutual inductance.
11. What are the factors affecting mutual inductance of a pair of coils? Define coefficient of coupling.
12. Describe the various methods of producing induced emf. Derive an expression for the instantaneous emf induced in a coil rotated in a magnetic field.

 

 

 

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Alternative Current-

1. Describe the principle construction and working of an AC generator. Draw neat labeled diagram
2. Define mean value of AC(over a half cycle) and derive an expression for it.
3. Define RMS value of AC and derive an expression for it. ()
4. Show that the average value of AC over a complete cycle is zero.
5. Show that the current and voltage are in phase in an ac circuit containing resistance only.
6. Deduce the phase relationship between current and voltage in an ac circuit containing inductor only.
7. Deduce the phase relationship between current and voltage in an ac circuit containing capacitor only.
8. Draw the phasor diagram showing voltage and current in LCR series circuit and derive an expression for the impedance
9. What do you mean by resonance in Series LCR circuit? Derive an expression for the frequency of resonance in LCR circuit.
10. Distinguish between resistance, reactance and impedance.
11. Define quality factor (Q factor) of resonance and derive an expression for it.
12. Describe the mechanism of electromagnetic oscillations in LC circuit and write expression for the frequency of oscillations produced.
13. Derive an expression for the average power in an ac circuit.
14. Define power factor. Deduce expression for it and explain wattless current?
15. Describe the principle construction theory and working of a transformer.
16. Describe the various losses in a transformer and explain how the losses can be minimized.

NOTES

NCERT EMI

 

NOTES AC

NCERT AC

EMI

SOLVED                     6.2, 6.3, 6.6, 6.7, 6.8, 6.9, 6.10

UNSOLVED      3,4,5,6,7, 8, 9, 10, 15, 16

 

AC

SOLVED            7.1, 7.2, 7.3, 7.5, 7.6, 7.7, 7.9 

UNSOLVED      1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 18, 20, 24, 25

 

DAY 16: Electromagnetic Induction; Faraday’s laws; Lenz’s law

 

 

1. What is Lenz’s law? Is this in accordance with the law of conservation of energy? How is it verified experiementally?
2. Which is the best method of reducing current in an a.c. circuit and why?
3. State Faraday’s Laws of electromagnetic induction. Express in mathematically.                        DAY 17: Self Induction, Mutual Induction(Transformer)
4. If the number of turns of a solenoid is doubled, keeping the other factors constant, how does the self inductance of the solenoid change?
5. If the self − inductance of an air core inductor increases from 0.01 mH to 10 mH on introducing an iron core into it, what is the relative permeability of the core used?
6. What is the self − inductance of a coil, in which magnetic flux of 40 milli weber is produced when 2A current flows through it?
7. Define the term self − induction. Write two factors on which the self − inductance of a coil depends.
8. How are eddy currents produced? Give two applications of eddy currents.
9. What are energy losses in a transformer? How can they be minimized?
10. How does the mutual inductance of a pair of coils change when (i) the distance between the coils is increased (ii) the number of turns in each coil is decreased Justify your answer in each case.
11. Predict the direction of induced current in resistance R is figure (a) and figure (b) given below. Give reason for your answer.
12. Explain phenomenon of mutual induction. Define coefficient of mutual induction. What are its units? Calculate coefficient of mutual induction between two long solenoids.
13. Explain with the help of a labelled diagram, the principle, construction and working of a transformer.                                                                                                 DAY 18: A.C.(LCR) , PHASOR DIAGRAM, RESISTOR, REACTANCE, IMPEDANCE
14. Name one device through which power consumed in an ac circuit is zero.
15. Sketch a graph showing the variation of reactance of a capacitor with frequency of applied voltage.
16. Give the phase difference between the applied ac voltage and the current in an LCR circuit at resonance.
17. The instantaneous voltage from a.c. source is given by E = 300 sin 314t. What is the r.m.s. voltage of the source?
18. Write two advantages of a.c. over d.c.
19. An inductor ‘L’ of reactance X_L, is connected in series with a bulb ‘B’ to an a.c. source as shown in figure. Briefly explain how does the brightness of the bulb change, when (i) number of turns of the inductors is reduced and (ii) a capacitor of reactance X_C = X_L is included in series in the same circuit.
20. Deduce an expression for impedance of series RLC circuit.
21. Distinguish between resistance, reactance and impedance for an a.c. circuit. Draw graphs showing variation for reactance of (i) a capacitor (ii) an inductor, with frequency of the applied voltage.
22. Derive an expression for the phase angle of an a.c. circuit with an inductor L, a capacitor C and a resistor R in series. Draw the phase diagram if the voltage across the capacitor is greater than that across the inductor. Obtain an expression for the resonant frequency of the circuit
23. LCR are in series with an AC source. Calculate power in such a circuit. Also obtain expression for resonant frequency . OR (a) Describe principle, construction and use of choke coil. (b) Describe Faraday’s laws of electromagnetic induction.
24. Draw the graphs to show the variation of (i) X_L and (ii) X_C with the frequency of the a.c. source used. A 200 V variable frequency a.c. source is connected to a series combination of L = 5, C = 80 μF and R = 40 Ω. Calculate (i) angular frequency of the source to get maximum current in the circuit, (ii) the current amplitude at resonance and (iii) the power dissipation in the circuit
25. What is meant by resonance in a L − C − R series a.c. circuit? State the essential conditions for resonance. A 50 mH inductor, a capacitor of capacitance 20 μF and a 10 ohm resistor are connected in series across 200 V a.c. source of variable frequency. Calculate (i) the resonant frequency of the circuit, (ii) current amplitude at resonance and (iii) maximum power dissipation.
26. Prove mathematically that the average power over a complete cycle of alternating current through an ideal inductor is zero.
27. Calculate the frequency of resonance of series RLC circuit. Hence define Q factor.
28. An ideal inductor consumes no power in an a.c. circuit. Explain.
29. An alternating voltage E = 200 sin 300 t is applied across a series combination of R = 10 W and inductor of 800 mH. Calculate (i) impedance of the circuit (ii) peak value of current in the circuit (iii) power factor of the circuit
30. Explain principle, construction and working of a.c. generator. How has it been modified to d.c. dynamo?
31. Prove that the power dissipated in an ideal resistor connector to an a.c. source is V²_eff /R. A capacitor, a resistor and a 40 mH inductor are connected in series to an a.c. source of frequency 60 Hz. Calculate the capacitance of the capacitor, if the current is in the phase with the voltage.
32. Show mathematically that the average power supplied to an ideal capacitor by a source over a complete cycle of a.c. is zero. A variable frequency 220 V alternating voltage source is connected across a series combination of L = 2.5 H, C = 160 mF and R = 50 W. Calculate (i) the angular frequency of the source which driven the circuit in resonance, (ii) the impedance of the circuit, and (iii) amplitude of the current at resonance.

BOOKLET

DAY 16 to 18

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