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ELECTO-MAGNETIC INDUCTION

1. Electro-Magnetic Induction:-

The phenomenon of electro magnetic induction is simply the production of electricity by a changing magnetic field associated with an electric circuit containing no source.

2. Faraday’s law of Electro-Magnetic Induction:-

The Faraday’s law of electro magnetic induction states that the induced e.m.f in a closed circuit (coil) is equal to the negative rate at which the magnetic flux through it changes.

Note:-

If the coil contains N turns, the ε is given by the formula.

3. Lenz’s Law:-

The induced current will appear in such a direction that it opposes the change that produced it.

4. Fleming’s Right Hand Rule:-

When the thumb, the fore finger and the central finger of the right hand are stretched mutually perpendicular to each other and are held such that the fore finger ‘F’ is along the direction of magnetic field (B) and the thumb is along the direction of motion of the linear conductor then the central finger points along the direction of the induced current ‘i’ or e.m.f

5. Dynamo:

A Dynamo is an electrical device which converts mechanical energy into electrical energy utilizing the phenomenon of electromagnetic induction.

6. Principle of dynamo:-

The principle of working of a dynamo is the law of electro magnetic induction.
7. Describe with a neat diagram showing the important parts of dynamo? Explain the working?

Parts:-

ABCD-armature, NS-permanent horse-shoe magnet, B1B2-carbon brushes,

Description:-

1. An AC dynamo consists of mainly four parts.

1. Armature.

2. Permanent magnet.

3. Two slip rings.

4. Two carbon brushes.

2. The armature ABCD consists of a coil made of insulated copper wire and is wound on a cylindrical soft-iron core. The armature is rotated rapidly about a horizontal axis perpendicular to the magnetic field.

3. NS is a permanent horse-shoe magnet. It provides a stationary magnetic field.
4. The ends of the armature coil are connected to two different slip rings S1 and S2 respectively. The rings are insulated from each other . These rings rotate along with the armature about the same axis as that of the coil.

5. Two carbon brushes B1 and B2 are always in contact with the slip rings S1 and S2 respectively.

6. The other two ends of B1 and B2 are connected to an external circuit containing load resistance ‘R’.

Working:-

7. When the armature ABCD is rotated in anti-clockwise direction, the magnetic flux (due to the magnet NS) linked with it changes.

8. As a result current is induced in the coil and flows through the load resistance R.

9. The rapid rotation of the armature in the dynamo generates a current or voltage in the external circuit whose direction alternates in each half cycle. Hence, such currents are called alternating currents.

8. Self -Induction:-

The production of an induced e.m.f in an isolated coil due to a change in the current in the same coil is called Self-Induction.

Where,
L is called Self-Inductance.

9. Self-Inductance:-

The self-Inductance of coil is numerically equal to the ratio between the induced e.m.f and the rate of change of current in the coil.

Note:-

1. The unit of Self-Inductance is “Henry”.

10. Mutual Induction:-

The Production of an induced e.m.f in one coil due to changes in current in another close by coil is known as Mutual Induction.

Where,
M is called Mutual Inductance.

11. Mutual Inductance:-

Mutual Inductance of a coil with respect to another coil is numerically equal to the ratio between the induced e.m.f in it and the rate of change of current in the other coil.

Note:-

1. The unit of Mutual Inductance is Henry.

12. Transformer:-

A transformer is an electrical device which either increases or decreases the magnitude of an alternating voltage by utilizing the phenomenon of electromagnetic induction.

13. Principle of a Transformer:-

A transformer works on the principle of electromagnetic Induction using mutual Inductance of two coils.

14. Explain the construction of a transformer with a diagram

Construction:-

1. The essential parts of a transformer are

1. Core.
2. Primary coil and
3. Secondary coil.
2. In its general form, a core (c) consists of a soft-iron or ferrite material.

3. This core is in the form of a rectangular frame built by placing thin sheets of iron one above the other. These sheets are laminated and therefore are insulated from each other.

Parts:-

C-core, P-primary coil, S-secondary coil.

Primary Coil:-

1. On one side of the rectangular core, an insulated copper wire is wound to make a coil of turns (n1).

2. If voltage is applied across this coil, it is called a primary (P) coil.

Secondary coil:-

On the opposite side of the rectangular core, another copper wire is wound to make a coil of turns (n2). If output voltage is delivered from this coil, it is called a Secondary (S) coil.

15. Explain the working of a transformer

1. As shown in the figure, a special transformer iron core contains two different number of turns of wire.

2. The coil to which energy is supplied, (AC voltage) is called as a Primary coil, and in which AC is induced is called a secondary coil.

Parts:-

C-core, P-primary coil, S-secondary coil.

3. A transformer having a smaller value secondary voltage than a primary voltage is known as Step-down transformer.

4. A Transformer having a higher value secondary voltage than a primary voltage is known as step-up transformer.

5. The voltage in secondary coil depends on the number of turns in it.

16. Types of transformers:-

There are two types of Transformers:-

1. Step-up transformers.

2. Step-down transformer.

1. Step-up transformer:-

The transformer with number of turns in the secondary coil higher than that in primary coil is called Step-up transformer.

2. Step-down transformer:-

The transformer with number of turns in the secondary coil smaller than that in primary coil is called Step-down transformer.

17. What do you mean by effective power Transmission? How does it take place?

Effective power transmission means an efficient transmission of electric power to the consumers at large distances from the power houses. Power transmission is carried out in the form of high voltage and low current so that energy losses are reduced. Pylons are the high towers to which high-tension transmission lines are connected. The network of high-tension supply system in a region is called a power grid. Therefore electricity is transmitted by a grid system using pylons.

18. How are power losses reduced in the power transmission?

Power transmission is carried out in the form of high voltage and low current so that energy losses are reduced.

19. Differences between Step-up and Step-down transformers:-

 Step-up transformer Step-down transformer 1.  Number of turns in secondary coil is more than the number of turns in primary coil. 1.  Number of turns in secondary coil is less than the number of turns in the primary coil. 2.  Output voltage is higher than input voltage. 2.  Output voltage is less than the input voltage.

20. Difference between the AC motor and DC motor:-

 AC motor DC motor 1.   If the arrangement uses alternating current it is called an AC motor. 1.  If the arrangement uses a DC source, it is called a DC electric motor. 2.  There is no need of commutator in AC motor. 2. It requires commutator.

21. Differences between alternating current and direct current?

 Alternating current Direct current 1.  Changes its direction of flow a number of times in a second. 1.  It is uni directional i.e., it always flows in one direction. 2.  It can be carried over longer distances. 2.  It cannot be carried over longer distances.

22. Differences between Ammeter and Voltmeter:-

 Ammeter Voltmeter 1.  It is used to measure current. 1.  It is used to measure potential difference or voltage. 2.  It is always connected in series in a circuit. 2.  It is always connected in parallel in a circuit.

23. Differences between power source and power consumer:-

 Power source Power consumer 1.  The device which supplies electrical energy is called power source. 1. The device which utilizes the energy supplied by a source is called power consumer. 2.  Examples:- cell, dynamo, generator etc.,. 2.  Examples:-bulb, fan, etc.,.

24. Name the devices working on the principle of electromagnetic induction.

1. Dynamo or generator.

2. Transformer.

25. Name the devices working on the principle of heating effect of electricity?

1. Electric Iron.
2. Immersion heater.
3. Electric stove and kettle.
4. Electric toaster.
5. Electric bulb.
6. Fuse.
26. Name the devices working on magnetic effect of electric current.

1. Galvalonometer.
2. Ammeter.
3. Voltmeter.
4. Electric motor.

II. Match the following:-

i.   Group-A                                                    Group-B

1. Unit of current                                          [b] a) Henry.

2. Unit of Resistance                                     [g] b) Ampere.

3. Unit of P.d                                                 [e] c) grams/coulomb.

4. Unit of Inductance                                    [a] d) coulomb

5. Unit of e.c.e                                               [c] e) Volt.

g) Ohm.

ii. Group-A                                                       Group-B

1. Rheostat                                                    [b] a) Converts high voltage
(AC) into low voltage.

2. Ammeter                                                    [d] b) to reduce or to build
current.

3. Voltmeter                                                    [g] c) converts electrical energy
into mechanical energy.

4. Transformer                                                 [a] d) measures currents.

5. Motor                                                           [ c] e) Detects the current.

f) Converts mechanical
energy into electrical
energy.

g) measures the p.d

iii. Group- A                                                          Group-B

1. Volt/Ampere                                                 [c] a) non Ohmic conductor

2. Ohm meter                                                   [d] b) Conductivity.

3. Semi conductor                                            [a] c) Ohm.

4. Mho/meter                                                   [b] d) Specific resistance.

5. Electric Conductor                                        [e] e) metal.

iv. Group-A                                                         Group-B

1. Joules constant                                             [e] a) Volt/Ampere.

2. Ohm                                                              [a] b) 1 calorie/gm0c.

3. Specific heat of water                                    [b] c) Resistance.

4.                                                                  [c] d) Coulomb/sec

5. Ampere                                                           [d] e) 4.18 Joules/calorie.

v.   Group-A                                                            Group-B

1. Electrical energy to mechanical energy           [e] a) Dynamo

2. Mechanical energy→Electrical energy.             [a] b) Transformer.

3. Increases AC voltage                                        [b] c) Decreases dissipation of
Electrical energy.

4. Iron core                                                            [c] d) Inductance.

5. Henry                                                                [d] e) Motor.

vi. Group-A                                                             Group-B

1. Series combination                                            [e] a) Ohm metre.

2. Parallel combination                                          [g] b) Semi-conductor.

3. Unit of specific resistance                                   [a] c)

4. Symbol of transformer                                         [f] d) mho-metre

5. Symbol of resistance                                            [c] e) same current passes.

f)

g) same p.d exists.

vii. Group-A                                                             Group-B

1. Electrolyte                                                         [a] a) Silver nitrate solution
(AgNO3)

2. Electro plating                                                   [e] b) unit of electrical energy.

3. Kilowatt Hour                                                    [b] c) Maxwell.

4. e.c.e                                                                   [g] d) Ampere.

5. Cork-Screw rule                                                 [c] e) Electrolysis.

f) unit of charge.

g) grams/coulomb.

viii. Group-A                                                               Group-B

1. Electric charges at rest                                       [c] a) Ampere.

2. Electric charges in motion                                 [b] b) Current electricity.

3. Potential difference                                           [e] c) Static electricity
.
4. Cell                                                                    [d] d) e.m.f.

5. Coulomb/second                                              [a] e) Volt.

ix. Group-A                                                               Group-B

1. Series                                                                 [b] a)watt.

2. Parallel                                                               [e] b)R1+R2=R

3. W                                                                       [d] c) KWH.

4. Electric unit                                                        [c] d) JQ

5. Joules/second                                                    [a] e) i=i1+i2.

x. Group-A                                                               Group-B

1. Electrolysis                                                      [d] a) Number.

2. e.c.e                                                                 [e] b) Electroplating.

3. Chemical equivalent                                        [a] c) Electrotyping.

4. Gold covering                                                  [b] d) voltameter.

5. Copy of letters                                                 [c] e) grams/coulomb.

III. Fill in the blanks:-

1. The study of electrical charges at rest is called static electricity.

2. The unit of electric current is Ampere.

3. Potential difference is measured in volts.

4. The direction of flow of positive charge is taken as the direction of conventional current.

5. Ammeter is used to measure current.

6. Voltmeter is used to measure the potential difference.

7. Tap-key is used to make and break and electric circuit.

8. The symbol of a battery is

9. When resistances are connected in series the total voltage is divided among them.

10. When resistances are connected in parallel the total current is divided among them.

11. The same current exists in all of them, when resistances are connected in series.

12. In parallel combination of resistances, the same p.d exists across all of them.

13. The equivalent resistance is more than any one of individual resistance when resistances are connected in series.

14. The effective resistance is less than any individual resistance when resistances are connected in parallel.

15. Magnetic induction at a point near a straight current carrying conductor is

16. The direction of force on the conductor in Fleming’s Left Hand Rule is represented by thumb finger.

17. Electric motor converts electric energy into Mechanical energy.

18. RPM stands for Rotations Per Minute.

19. The rectangular coil in the electric motor can be called as Armature.

20. The study of electrical charges at rest is called static electricity.

21. The study of various effects of electrical charges in motion is called Current electricity.

22. If a net charge of one coulomb passes through any cross-section of a conductor in time of one second then the current is called 1 Ampere.

23. The work done in moving a single unit positive charge from infinity to that point is called electric potential.

24. The amount of work done by the seat (cell) on the charge carrier to force to go to the point of higher potential is electro motive force.

25. e.m.f. is measured in volts.

26. If three cells of each of potential difference 1.2V, 1.5 V and 1.7V are connected in parallel then the effective pd is 1.7 V.

27. The long chains of decorative bulbs are connected in series.

28. The opposition to flow of the current in an electric conductor is resistance.

29. The device used in a circuit to regulate the current through it is Rheostat.

30. The unit of specific resistance is Ohm metre.

31. The unit of conductivity is Mho/meter

32. The effective resistance in parallel combination of resistance is less than any of the individual resistance.

33. As the temperature of a conductor increases the resistance increases.

34. The arrangement in electric circuit that prevents short circuit is fuse.

35. The heat developed due to the conversion of any form of work or energy is called Joule heat.

36. 1 KWH =36×105 watt second.

37. The process of decomposition of a chemical compound in a solution when an electric current passes through it is electrolysis.

38. The vessel which contains electrolyte and allows electrolysis to take place is called voltameter or electrolytic cell.

39. A current carrying rectangular coil behaves as magnet.

40. The direction of the current in the Fleming’s Left Hand Rule is indicated by central finger.

41. 1 Joule=1 volt x 1 ampere x 1 second.

42. The production of an induced e.m.f due to the change in current in another coil near by is known as Mutual Induction.

43. The direction of induced e.m.f is given by Lenz’s law.

44. Ammeter is always connected in series.

45. Voltmeter is always connected in parallel.

46. Dynamo converts Mechanical energy to electrical energy.

47. The mass of substance deposited or liberated from a solution by passage of one coulomb of electricity in unit time is electro chemical equivalent.

48. Transformer is a device used to convert alternating high voltage into low voltage or vice-versa.

49. A Galvanometer is an instrument used for measuring small currents.

50. 1 Joule/ 1 second=1 Watt.

51. 1 KWH=36×105 Joules.

52. The reciprocal of specific resistance is called conductance.

53. In series combination of cells, the total voltage increases.

54. In parallel combination of cells, the total voltage is constant.

55. Resistance of Ohmic conductor increases with increase in temperature.

56. Transformers works on AC only.

57. Construction of Galvanometer is constructed using Fleming’s Left Hand Rule.

58. An instrument used to reverse the direction of current is commutator.

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