2nd Year Physics Chapter 15 Electromagnetic Induction Notes MCQs Solutions

physics 12th notes mcqs chapter 15

1. In an ideal case, the rate of change of flux in the secondary coil of transformer is:

 
 
 
 

2. Lenz’s law provides a relation between:

 
 
 
 

3. If the current in the coil itself is increased by rheostat, the emf induced will be:

 
 
 
 

4. The SI unit of self inductance is:

 
 
 
 

5. One Henry is equal to

 
 
 
 

6. A transformer is a device which

 
 
 
 

7. If we make the magnetic field stronger, the value of induced current is:

 
 
 
 

8. The energy stored in its magnetic field is:

 
 
 
 

9. The SI unit of magnetic induction is

 
 
 
 

10. Lenz’s law presented in:               

 
 
 
 

11. The mutual induction between the two coils depends upon:

 
 
 
 

12. The induced current in a circuit depends upon:

 
 
 
 

13. Changing current in a coil induces an emf in itself is called

 
 
 
 

14. Faraday’s law was deduced in:

 
 
 
 

15. Lenz was a physicist.                      

 
 
 
 

16. When back emf in motor is zero, it draws

 
 
 
 

17. Faraday’s law of electromagnetic induction has been used in the construction of:

 
 
 
 

18. The principle of an alternating current generator is based on:

 
 
 
 

19. The statement “ the direction of an induced current is
such as to oppose the cause which produces it “ is known as

 
 
 
 

20. For the use of an electric lamp of low voltage on A.C main of high voltage, we use the device called

 
 
 
 

21. An alternating current is converted into direct current by:

 
 
 
 

22. The negative sign in the equation  can be explained by:

 
 
 
 

23. When the current in a coil changes from 0 to 10 A in 0.025s, an average emf induced in a neighboring coil is 600 v, the Mutual inductance for two coils is:

 
 
 
 

24. The main cause of power loss in transformer is:          

 
 
 
 

25. An alternating current is converted into direct current by a

 
 
 
 

26. When a conductor move across a magnetic field, an emf is set up, this emf is called

 
 
 
 

27. Slip rings are used in:       

 
 
 
 

28. Energy stored per unit volume inside the solenoid is called:

 
 
 
 

29. The current produced due to electromagnetic induction is called:

 
 
 
 

30. Mutual inductance has practical role in the performance
of the

 
 
 
 

31. The negative sign in the equation shows that the induced emf in such a direction that it: At

 
 
 
 

32. The negative sign in the expression ε=-vBL shows that the angle between the direction of L and (VxB) is

 
 
 
 

33. Then the current flows:

 
 
 
 

34. One Henry can be defined as

 
 
 
 

35. The mutual Inductance between two coils depends upon their

 
 
 
 

36. The Lenz’s Law fulfils:

 
 
 
 

37. The Lenz’s law refers to:              

 
 
 
 

38. The windings of an electromagnet used in motors are called:

 
 
 
 

39. This induced emfis in such a direction that:

 
 
 
 

40. The practical application of the phenomenon of mutual induction is:

 
 
 
 

41. Energy density in an inductor is:

 
 
 
 

42. An alternating current is that which:

 
 
 
 

43. Which one is not present in AC generator?

 
 
 
 

44. Magnetic potential energy stored in inductors depends upon:

 
 
 
 

45. The symbol Um represents:                     

 
 
 
 

46. Lenz’s Law deals with

 
 
 
 

47. The induced current in a loop can be increased by:

 
 
 
 

48. An electric motor converts:         

 
 
 
 

49. In a practical transformer, the output is always:           

 
 
 
 

50. A coil of wire is also called:

 
 
 
 

51. The self inductance is expressed by the relation L=

 
 
 
 

52. If a closed metallic loop is moved across a magnetic field then:

 
 
 
 

53. The energy stored in an inductor is given by

 
 
 
 

54. The SI unit of mutual inductance is:

 
 
 
 

55. Which one of the following produced first:

 
 
 
 

56. The coil from which the power is delivered to the circuit is called:

 
 
 
 

57. A generator running in reverse direction may be called as:

 
 
 
 

58. The back emf of a motor can be expressed as

 
 
 
 

59. If magnetic field is doubled then magnetic energy density becomes:

 
 
 
 

60. The device which converts A.C. voltage of one magnitude into the other required magnitude of the A.C voltage is called

 
 
 
 

61. When the back emf in a generator is maximum, it draws

 
 
 
 

62. The jerks in DC motors are created by use of

 
 
 
 

63. When a constant current flows in primary of transformer then emf induced across the secondary of transformer is

 
 
 
 

64. The emf induced in the secondary coil is directly proportional to:

 
 
 
 

65. A.C is converted into D.C by:

 
 
 
 

66. In magnet-coil experiment, emfcan be produced by:

 
 
 
 

67. Henry is the unit of

 
 
 
 

68. Which phenomenon of the following is produced first

 
 
 
 

69. A changing electric flux Creates

 
 
 
 

70. The Lenz’s law refers to:

 
 
 
 

71. The direction of induced current is always so as to oppose the change which causes the current, this is the statement of:

 
 
 
 

72. Commutator was invented in:                 

 
 
 
 

73. The practical application of phenomenon of mutual
induction is

 
 
 
 

74. The self induction does not depend upon:        

 
 
 
 

75. The emf produced by the motion of a coil across the magnetic field is called:

 
 
 
 

76. The principle of A.C generator is

 
 
 
 

77. Work can be stored in an inductor as:

 
 
 
 

78. Lenz’s law is also statement of:  

 
 
 
 

79. If the load in the external circuit is greater, the current supplied by the generator is:

 
 
 
 

80. The induced current can be increased by.

 
 
 
 

81. The energy can be stored in the:             

 
 
 
 

82. The direction of the induced emf during electromagnetic induction can be determined by the use of:

 
 
 
 

83. Which of the following converts electrical energy into
mechanical energy

 
 
 
 

84. Unit of self inductance is

 
 
 
 

85. The negative sign with induced emf in Faraday’s law is in
accordance with

 
 
 
 

86. If the speed of rotation of a generator is doubled the output voltage will be:

 
 
 
 

87. The principle of electric generator is based on:

 
 
 
 

88. When we study the phenomenon mutual induction between two coils, the primary coil consists of:

 
 
 
 

89. Lenz’s law is in accordance with law of conservation of

 
 
 
 

90. The SI unit of self inductance or mutual inductance is

 
 
 
 

91. Self-induced emf is sometimes called as

 
 
 
 

92. When a coil is moved in a uniform magnetic field , an induced emf is produced due to change of

 
 
 
 

93. An electric motor is device which converts

 
 
 
 

94. A transformer has:

 
 
 
 

95. A magnetic compass will be deflected ifit is kept near a:

 
 
 
 

96. The coils of a transformer are:    

 
 
 
 

97. The Phenomenon by which an induced emf is produced in the conductor due to change of magnetic flux in it is called:

 
 
 
 

98. Michael Faraday and Joseph Henry belongs to:

 
 
 
 

99. A device consisting of two coils wound on an iron core is called

 
 
 
 

100. Component in generator which consumes energy is called.

 
 
 
 

101. The work is stored in an inductor as:

 
 
 
 

102. Energy density is defined as

 
 
 
 

103. If motor is over loaded then magnitude of back emf

 
 
 
 

104. The only difference between construction of D.C. generator and an A.C. generator is that of

 
 
 
 

105. Eddy currents are produced in a material when it is placed

 
 
 
 

106. An electric motor consists of:                 

 
 
 
 

107. The experiments show that whenever there is a change in the magnetic flux linked with a loop or closed circuit
there is always

 
 
 
 

108. According to Faraday’s law of electromagnetic induction the induced emf in a coil can be mathematically
expressed as

 
 
 
 

109. Because of their self inductance, coils were known as

 
 
 
 

110. In order to minimize the power loss during transmission:

 
 
 
 

111. The inductance can be increased by winding the wire around a core made of

 
 
 
 

112. When we study mutual induction between two coils, the secondary coil circuit consists of:

 
 
 
 

113. The practical Illustration of the phenomenon of mutual induction in what among the following:

 
 
 
 

114. The motional emf developed in a conductor depends upon

 
 
 
 

115. When current I passes through a resistance R, the power loss due to heating effect is:

 
 
 
 

116. Emf produced by A.C generator depends upon:          

 
 
 
 

117. A 50mH coil carries a current of 2A. the energy stored in
its magnetic field is

 
 
 
 

118. The devices in the circuit that consume electrical energy are known as:

 
 
 
 

119. When the conductor is moved with its length parallel to the lines of magnetic field:

 
 
 
 

120. When motor is just started, back emf is almost:

 
 
 
 

121. The fact that electric current through a conductor
produces magnetic field around it was discovered by

 
 
 
 

122. A wire loop is moved parallel to a uniform magnetic field.
The induced emf in the loop

 
 
 
 

123. Coramutators are used in

 
 
 
 

124. A rod of length 20 m is moving with 20 m sec⁻¹ in a direction perpendicular to magnetic of 20 T the value of emf is

 
 
 
 

125. A current which reverses its direction in each second is called:

 
 
 
 

126. The current flowing through a coil due to induced emf in
it depends upon

 
 
 
 

127. The maximum emf generated in a generator is

 
 
 
 

128. The product of induced current and resistance is always:

 
 
 
 

129. Electromagnetic induction is the phenomenon in which
an emf is induced in the coil due to the change of flux through it when

 
 
 
 

130. An ernf is set up in a conductor when it:

 
 
 
 

131. A transformer works on the principle of

 
 
 
 

132. A device that converts mechanical energy into electrical energy is called:

 
 
 
 

133. Which of the following is scalar:

 
 
 
 

134. if velocity of rod is 1 ms⁻¹, then induced emf in the rod will be given by

 
 
 
 

135. A.C. can be measured with the help of

 
 
 
 

136. Alternating current generator use:                     

 
 
 
 

137. Electromagnetic induction obeys law of conservation of

 
 
 
 

138. One henry is equal to:

 
 
 
 

139. Commutator was invented by:

 
 
 
 

140. The ratio of self induced emf to the rate of change of
current in the coil is known as

 
 
 
 

141. A transformer consists of an iron core with

 
 
 
 

142. If the plane of the generator coil is parallel to field, then emf induced in coil is

 
 
 
 

143. Inductors behaves like the:

 
 
 
 

144. The knowledge of electromagnetic induction has been used in construction of:

 
 
 
 

145. The phenomenon of production of induced emf is called:

 
 
 
 

146. The unit of induced emf is:

 
 
 
 

147. If the number of turn in a coil is increased metallic ring to 3 times than its initial number, then the magnetic flux linked with is:

 
 
 
 

148. A transformer has no:                  

 
 
 
 

149. If velocity of conductor moving through a magnetic field B
is zero, then its motional emf will be

 
 
 
 

150. The process in which a change of current in one coil
causes an induced emf in another coil nearby it is called

 
 
 
 

151. A transformer is used to change

 
 
 
 

152. A device which converts electrical energy into mechanical energy is called:

 
 
 
 

153. Energy can be stored in a magnetic field of:     

 
 
 
 

154. A transformer consists of an iron core with:

 
 
 
 

155. A transformer steps 220 V to 40 V. if the secondary turns are 40
and primary turns are

 
 
 
 

156. Lenz’s law does not violated the principle of:

 
 
 
 

157. When we say that Lenz law refers to induced currents, it means that we can apply it directly to:

 
 
 
 

158. The current produced by moving a loop (wire) across the magnetic field is called:

 
 
 
 

159. The ratio of the emf in the secondary coil to the rate of change of current in the primary coil is known as:

 
 
 
 

160. When the rate of change of current in a coil is unity then the induced emf will beequal to:

 
 
 
 

161. A coil of constant area is placed in a constant magnetic field, an induced current is produced in the coil when:

 
 
 
 

162. Lenz’s law is in accordance with the Law of Conservation of:

 
 
 
 

163. Alternating emf is produced by rotating a coil of wire in:

 
 
 
 

164. The induced emf in a circuit depends upon:

 
 
 
 

165. Eddy currents produced in the core of transformer are responsible for:

 
 
 
 

166. Who invented commutator:                     

 
 
 
 

167. The mutual induction between two coils depends upon:

 
 
 
 

168. The phenomenon in which a change of current in one coil induces an emf in the other coil will be known as:

 
 
 
 

169. The direction of magnetic induction in the region P.

 
 
 
 

170. The device whose working based on this principle is:

 
 
 
 

171. The phenomenon of producing emf in a coil due to the change of current in itself is called:

 
 
 
 

172. Commutators was invented in:

 
 
 
 

173. The law of electromagnetic induction is related to:

 
 
 
 

174. Inductance is measured in

 
 
 
 

175. The emf produced is

 
 
 
 

176. The induced emf across the conductor is:

 
 
 
 

177. The motional emf depends upon the

 
 
 
 

178. An Inductor may store energy in its

 
 
 
 

179. Mutual inductance of coil depends upon

 
 
 
 

180. A generator is device that converts

 
 
 
 

181. A wire carrying the current placed in a magnetic field experience a force, this is the basic principle of:

 
 
 
 

182. If one coil is wound on an iron core, the flux through it will:

 
 
 
 

183. Milli-Henry is the unit of

 
 
 
 

184. The rate of change of magnetic flux is directly proportional to the induced emf is called:

 
 
 
 

185. The ratio of the self-induced emf to the rate of change of current in the coil will be called :

 
 
 
 

186. Which one of the following is not present in A.C. generator

 
 
 
 

Short Questions

1. A coil of wire in the xy plane with a magnetic field directed along the Y-axis.Around which of the three co-ordinate axes should the coil be rotated in order to generate an emf and a current in the coil?
2. A glance at a dynmo will indicate whether it has sliprings or commutators.How will this information enable one to know whether the machine is an A.C. or D.C.generator?
3. A light metallic is released from above into a vertical bar magnet viewed from above does the current flow clockwise or anticlockwise in the ring?
4. A square loop of wire is moving through a uniform magnet field.The normal to the loop is oriented parallel to the magnetic field.Is an emf induced in the loop?Give a reason for your answer?
5. A suspended magnet is oscillating freely in a horizontal plane.The oscillations are strongly damped when a metal plate is placed under magnet.Explain why this occurs?
6. Can a current carrying coil be used as a compass?Explain.
7. Can a D.C motor be turned into a D.C.generator?
8. Can a step – up transformer increase the power.(b) In a transformer there is no transfer of charge from the primary to the secondary,How is then the power transferred?
9. Can a step up transformer increase the power level?
10. Can an efficient transformer step- up energy?
11. Can an electric motor be used to drive an electric generator with the output from the generator being used to operate the motor?
12. cm is moving at a speed of 0.25 m sec⁻¹ in a direction perpendicular to a point 0.50 T magnetic field. What is the emf produced in the moving rod ?
13. Define eddy current ?
14. Define efficiency of a transformer?
15. Define electromagnetic induction?
16. Define henry?
17. Define load in an electrical circuit ?
18. Define motional emf?
19. Define self – inductance and give its unit?
20. Define the phenomenon of self inductance ?
21. Define the term energy density ?
22. Derive the dimensional formula for co–efficient of self – inductance?
23. Derive the dimensional formula for the self inductance ?
24. Describe some uses of step – down transformers?
25. Differentiate between an A.C and D.C currents?
26. Discuss briefly that the Lenz’s law is exactly in accordance to the law of the law of conservation of energy?
27. Does the induced current depend on the resistance of the circuit?
28. Does the induced emf always act to decrease the magnetic flux through a circuit?
29. Does the induced emf in a circuit depend on the resistance of the circuit?Does the induced current depend upon the resistance of the circuit?
30. Does the induced emf in a circuit depends on the resistance of the circuit ?
31. Does the inductance of a coil depend on the current in the coil?What factors affect the inductance of a coil?
32. Does the voltage output of a generator change if its speed of rotation is increased?Explain.
33. Four unmarked wires emerge from a transformer.What steps would you take to determine the turns ratio?
34. Give a mathematical relation for the energy density in an inductor ?
35. How can teh power losses be minimized in a transformer?
36. How can the concept of electro – magnetic induction be used to apply breaks to fast moving automobile?
37. How is the armature rotated in commercial generators?
38. How is the efficiency of Transformer increased?
39. How power loss due to eddy currents in a transformer can be reduced?
40. How the back emf of a motor can be expressed?
41. How the magnetic field in the D.C motor is provided?
42. How would you position a flat loop of wire in a changing magnetic field so that there is no emf induced in the loop?
43. In a certain region the earth’s magnetic field point vertically down.When a plane flies due north which wingtip is possibly charged?
44. In what three ways can a voltage be induced in a wire?
45. Is it possible to change both the area and the magnetic field passing through the loop and still not have an induced emf in the loop?
46. Is the law of conservation of energy is applicable to the phenomena of induction ?
47. Name the factors on which self inductance depends ?
48. Name the factors upon which the self – inductance depends?
49. Name the main parts of an A.C generator ?
50. On which principle transformer works ?
51. rev per min. What is the back emf when the motor turns 3360 rev per min ?
52. State Faraday’s law of electromagnetic induction ?
53. State Lenz’s law ?
54. The self – inductance of an air core is independent of the value of the current in the coil.This is not true for an iron – core coil.Explain?
55. What are similarities between a motor and a generator?What are the differences?
56. What are the main causes of power loss in a transformer?
57. What happened when any motor is over loaded ?
58. What is a back emf effect in motors?
59. What is a commutator ?
60. What is a generator ?
61. What is a transformer ?
62. What is an A.C. generator ?
63. What is an inductor ?
64. What is back emf in a motor which is just started?What is induced emf in a speedy motor?
65. What is D.C generator ?
66. What is difference between an A.C generator and D.C generator?
67. What is difference between step up transformer and step down transformer?
68. What is electromagnetic induction ?
69. What is henry?
70. What is hysteresis?
71. What is induced current ?
72. What is induced emf ?
73. What is mutual induction ?
74. What is self induction ?
75. What is the induced emf produced during the phenomenon of self induction ?
76. What is the magnitude of back emf in a transformer?
77. What is the net current flowing through a coil of a motor in the presence of a back emf?
78. What is the SI unit of motional emf ?
79. What is the SI unit of mutual inductance ?
80. What is the SI unit of self inductance?
81. What is the use of self – inductance in A.C circuits?
82. What is the wave form of A.C voltage or current ?
83. What is the working principle of a D.C motor?
84. What is the working principle of a generator?
85. What is transformer?
86. When an electic motor such an electric drill is being used does it also act as a generator?If so what is the consequence of this?
87. When the primary of a transformer is connected to a.c. mains the current it. (a) is very small if the secondary circuit is open but (b) increases whether the secondary circuit is closed Explain these facts.
88. When the switch in the circuit is closed the current is established in the coil and the metal ring jumps upward. Why?
89. Whether an inductor coil may appear like a solenoid?
90. Whether energy can be stored in the magnetic field of an inductor ?
91. Whether inductors capacitor?
92. Whether transformer obeys the law of conservation of power?
93. Why self induced emf is also called as back emf?
94. Will the out put voltage of a generator change if its speed of rotation is increased?

Long Questions

1. Define electromagnetic induction.
2. What is induced emf and induced current? Explain with different experiments.
3. Define motional emf and derive a relation for it.
4. State and explain Faraday’s law of electromagnetic induction. Also calculate induced emf.
5. State and explain Lenz’s law and direction of induced emf.
6. Explain the phenomenon mutual induction.
7. Explain the phenomenon self induction.
8. What type of energy is stored in an inductor? Find the relations for the energy and energy density in an inductor.
9. Describe the principle, construction and working of an alternating current generator.
10. What is D.C. generator?
11. Explain back motor effect in generators.
12. What is D.C. motor?
13. Explain the back emf effect in motors.
14. Describe construction, principle and working of a transformer.
15. How the power is lost in transformer?
16. An EMF of 0.45V is induced between the ends of a metal bar moving through a magnetic field of 0.22T. What field strength would be needed on EMF of 5 V bet. The ends of the bar, assuming that all other factors remain the same?
17. The flux density B in a region between the pole faces of a horse shoe magnet 0.5 wb/m² directed vertically downwards. Find the EMF induced in a straight wire 5cm long, perpendicular to B when it is moved in a direction at an angle of 60degree with the horizontal with a speed of 100cms⁻¹.
18. A coil of wire has 10 loop. Each loop has an area of 5 x 10⁻³m². A magnetic field perpendicular to the surface of each loop at all times. If the magnetic field is charged from 0.05T to 0.06T in 0.1 sec. Find the average EMF induced in the coil during this time.
19. A circular coil has 15 turns of radius 2cm each. The plane of the coil is inclined at 40 degree to a uniform magnetic field of 0.2T. If the field is increased to 0.5T in 0.2 sec, find the magnitude of the induced EMF.
20. Two coils are placed side by side. An EMF of 0.8V is observed in one coil when the current is changing at the rate of 200 As⁻¹ in the other coil. What is the mutual inductance of the coils?
21. A pair of adjacent coils has a mutual inductance of 0.1H. If the current in the primary changes from 0 to 10 A in 0.25s, what is the average induced EMF in the secondary? What is the change in flux in it if the secondary has 500 turns?
22. A solenoid has 250 turns and its self inductance is 2.4 mH. What is the flux through each turn when the current is 2A? What is the induced EMF when the current changes at 20 As⁻¹?
23. A solenoid of length 8cm and cross sectional area 0.5cm² turns. Find the self inductance of the solenoid when the core is air. If the current in the solenoid increases through 5A in 0.2 sec, find the magnitude of induced EMF in it.
24. When current through a cell changes from 100 mA to 200 mA in 0.005 sec, an induced EMF of 40 mV is produced in the coil. (a) What is the self inductance of the coil? (b) Find the increase in the energy stored in the coil.
25. Like any field, the Earth’s magnetic field stores energy. Find the magnetic energy stored in a space where strength of earth’s field is 7 x 10⁻⁵ T, if the space occupies an area of 10 x 10⁸m² and has a height of 750m.
26. A square coil of side 16cm has 200 turns and rotates in uniform magnetic field of magnitude 0.05 T. If the peak EMF is 12 V, what is the angular velocity of the cell?
27. A generator has a rectangular coil consisting of 360 turns. The coil rotates at 420 rev per min in 0.14 T magnetic field. The peak value of EMF produced by the generator is 50 V. If the coil is 5 cm wide, find the length of the side of the coil.
28. It is desired to make an A.C generator that can produce an EMF of 5kV with 50Hz frequency. A coil of area 1m² consisting of 200 turns is used as armature. What should be the magnitude of the magnetic field in which the coil rotates?
29. The back EMF in a motor is 120 V when the motor is turning at 1680 rev/min. What is the back EMF when the motor turns at 3360 rev/min?
30. A D.C motor operates at 240V and has a resistance of 0.5 ohm. When the motor is running at normal speed, the armature is 15A. Find the back EMF in the armature.
31. A copper ring has radius of 4cm and resistance of 1 milli ohm. A magnetic field applied over the ring, perpendicular to its plane. If the magnetic field increases from 0.2 T to 0.4 T in a time interval of 5 x 10⁻³s. What is the current in the ring during?
32. A coil of 10 turns and 35 cm² area is in a perpendicular magnetic field of 0.5T. The coil is pulled out of the field in 1s. Find the induced EMF in the coil as it is pulled out of the field.
33. An ideal step down transformer is connected to main supply of 240V. It is desired to operate a 12V, 30W lamp. Find the current in the primary and the transformation ratio?

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