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| Physics 12th Chapter 15 - Electromagnetic Induction |
Physics 12th Chapter 15 - Electromagnetic Induction Solved MCQs, Important Short Questions and Long Questions Bank
MCQs
Please select the right answer.
1. Commutators was invented in:
2. A 50mH coil carries a current of 2A. the energy stored in its magnetic field is
3. A changing electric flux Creates
4. A coil of constant area is placed in a constant magnetic field, an induced current is produced in the coil when:
5. A coil of wire is also called:
6. A current which reverses its direction in each second is called:
7. A device consisting of two coils wound on an iron core is called
8. A device that converts mechanical energy into electrical energy is called:
9. A device which converts electrical energy into mechanical energy is called:
10. A generator is device that converts
11. A generator running in reverse direction may be called as:
12. A magnetic compass will be deflected ifit is kept near a:
13. 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
14. A transformer consists of an iron core with
15. A transformer consists of an iron core with:
16. A transformer has no:
17. A transformer has:
18. A transformer is a device which
19. A transformer is used to change
20. A transformer steps 220 V to 40 V. if the secondary turns are 40 and primary turns are
21. A transformer works on the principle of
22. A wire carrying the current placed in a magnetic field experience a force, this is the basic principle of:
23. A wire loop is moved parallel to a uniform magnetic field. The induced emf in the loop
24. A.C is converted into D.C by:
25. A.C. can be measured with the help of
26. According to Faraday’s law of electromagnetic induction the induced emf in a coil can be mathematically expressed as
27. Alternating current generator use:
28. Alternating emf is produced by rotating a coil of wire in:
29. An alternating current is converted into direct current by a
30. An alternating current is converted into direct current by:
31. An alternating current is that which:
32. An electric motor consists of:
33. An electric motor converts:
34. An electric motor is device which converts
35. An ernf is set up in a conductor when it:
36. An Inductor may store energy in its
37. Because of their self inductance, coils were known as
38. Changing current in a coil induces an emf in itself is called
39. Commutator was invented by:
40. Commutator was invented in:
41. Component in generator which consumes energy is called.
42. Coramutators are used in
43. Eddy currents are produced in a material when it is placed
44. Eddy currents produced in the core of transformer are responsible for:
45. Electromagnetic induction is the phenomenon in which an emf is induced in the coil due to the change of flux through it when
46. Electromagnetic induction obeys law of conservation of
47. Emf produced by A.C generator depends upon:
48. Energy can be stored in a magnetic field of:
49. Energy density in an inductor is:
50. Energy density is defined as
51. Energy stored per unit volume inside the solenoid is called:
52. Faraday’s law of electromagnetic induction has been used in the construction of:
53. Faraday’s law was deduced in:
54. For the use of an electric lamp of low voltage on A.C main of high voltage, we use the device called
55. Henry is the unit of
56. If a closed metallic loop is moved across a magnetic field then:
57. If magnetic field is doubled then magnetic energy density becomes:
58. If motor is over loaded then magnitude of back emf
59. If one coil is wound on an iron core, the flux through it will:
60. If the current in the coil itself is increased by rheostat, the emf induced will be:
61. If the load in the external circuit is greater, the current supplied by the generator is:
62. 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:
63. If the plane of the generator coil is parallel to field, then emf induced in coil is
64. If the speed of rotation of a generator is doubled the output voltage will be:
65. If velocity of conductor moving through a magnetic field B is zero, then its motional emf will be
66. if velocity of rod is 1 ms⁻¹, then induced emf in the rod will be given by
67. If we make the magnetic field stronger, the value of induced current is:
68. In a practical transformer, the output is always:
69. In an ideal case, the rate of change of flux in the secondary coil of transformer is:
70. In magnet-coil experiment, emfcan be produced by:
71. In order to minimize the power loss during transmission:
72. Inductance is measured in
73. Inductors behaves like the:
74. Lenz was a physicist.
75. Lenz’s Law deals with
76. Lenz’s law does not violated the principle of:
77. Lenz’s law is also statement of:
78. Lenz’s law is in accordance with law of conservation of
79. Lenz’s law presented in:
80. Lenz’s law provides a relation between:
81. Lenz's law is in accordance with the Law of Conservation of:
82. Magnetic potential energy stored in inductors depends upon:
83. Michael Faraday and Joseph Henry belongs to:
84. Milli-Henry is the unit of
85. Mutual inductance has practical role in the performance of the
86. Mutual inductance of coil depends upon
87. One Henry can be defined as
88. One Henry is equal to
89. One henry is equal to:
90. Self-induced emf is sometimes called as
91. Slip rings are used in:
92. The practical application of phenomenon of mutual induction is
93. The back emf of a motor can be expressed as
94. The coil from which the power is delivered to the circuit is called:
95. The coils of a transformer are:
96. The current flowing through a coil due to induced emf in it depends upon
97. The current produced by moving a loop (wire) across the magnetic field is called:
98. The current produced due to electromagnetic induction is called:
99. The device which converts A.C. voltage of one magnitude into the other required magnitude of the A.C voltage is called
100. The device whose working based on this principle is:
101. The devices in the circuit that consume electrical energy are known as:
102. The direction of induced current is always so as to oppose the change which causes the current, this is the statement of:
103. The direction of magnetic induction in the region P.
104. The direction of the induced emf during electromagnetic induction can be determined by the use of:
105. The emf induced in the secondary coil is directly proportional to:
106. The emf produced by the motion of a coil across the magnetic field is called:
107. The emf produced is
108. The energy can be stored in the:
109. The energy stored in an inductor is given by
110. The energy stored in its magnetic field is:
111. The experiments show that whenever there is a change in the magnetic flux linked with a loop or closed circuit there is always
112. The fact that electric current through a conductor produces magnetic field around it was discovered by
113. The induced current can be increased by.
114. The induced current in a circuit depends upon:
115. The induced current in a loop can be increased by:
116. The induced emf across the conductor is:
117. The induced emf in a circuit depends upon:
118. The inductance can be increased by winding the wire around a core made of
119. The jerks in DC motors are created by use of
120. The knowledge of electromagnetic induction has been used in construction of:
121. The law of electromagnetic induction is related to:
122. The Lenz’s law refers to:
123. The Lenz's Law fulfils:
124. The Lenz's law refers to:
125. The main cause of power loss in transformer is:
126. The maximum emf generated in a generator is
127. The motional emf depends upon the
128. The motional emf developed in a conductor depends upon
129. The mutual Inductance between two coils depends upon their
130. The mutual induction between the two coils depends upon:
131. The mutual induction between two coils depends upon:
132. The negative sign in the equation shows that the induced emf in such a direction that it: At
133. The negative sign in the equation can be explained by:
134. The negative sign in the expression ε=-vBL shows that the angle between the direction of L and (VxB) is
135. The negative sign with induced emf in Faraday’s law is in accordance with
136. The only difference between construction of D.C. generator and an A.C. generator is that of
137. The Phenomenon by which an induced emf is produced in the conductor due to change of magnetic flux in it is called:
138. The phenomenon in which a change of current in one coil induces an emf in the other coil will be known as:
139. The phenomenon of producing emf in a coil due to the change of current in itself is called:
140. The phenomenon of production of induced emf is called:
141. The practical application of the phenomenon of mutual induction is:
142. The practical Illustration of the phenomenon of mutual induction in what among the following:
143. The principle of A.C generator is
144. The principle of an alternating current generator is based on:
145. The principle of electric generator is based on:
146. The process in which a change of current in one coil causes an induced emf in another coil nearby it is called
147. The product of induced current and resistance is always:
148. The rate of change of magnetic flux is directly proportional to the induced emf is called:
149. The ratio of self induced emf to the rate of change of current in the coil is known as
150. The ratio of the emf in the secondary coil to the rate of change of current in the primary coil is known as:
151. The ratio of the self-induced emf to the rate of change of current in the coil will be called :
152. The self inductance is expressed by the relation L=
153. The self induction does not depend upon:
154. The SI unit of magnetic induction is
155. The SI unit of mutual inductance is:
156. The SI unit of self inductance is:
157. The SI unit of self inductance or mutual inductance is
158. The statement “ the direction of an induced current is such as to oppose the cause which produces it “ is known as
159. The symbol Um represents:
160. The unit of induced emf is:
161. The windings of an electromagnet used in motors are called:
162. The work is stored in an inductor as:
163. Then the current flows:
164. This induced emfis in such a direction that:
165. Unit of self inductance is
166. When a coil is moved in a uniform magnetic field , an induced emf is produced due to change of
167. When a conductor move across a magnetic field, an emf is set up, this emf is called
168. When a constant current flows in primary of transformer then emf induced across the secondary of transformer is
169. When back emf in motor is zero, it draws
170. When current I passes through a resistance R, the power loss due to heating effect is:
171. When motor is just started, back emf is almost:
172. When the back emf in a generator is maximum, it draws
173. When the conductor is moved with its length parallel to the lines of magnetic field:
174. 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:
175. When the rate of change of current in a coil is unity then the induced emf will beequal to:
176. When we say that Lenz law refers to induced currents, it means that we can apply it directly to:
177. When we study mutual induction between two coils, the secondary coil circuit consists of:
178. When we study the phenomenon mutual induction between two coils, the primary coil consists of:
179. Which of the following converts electrical energy into mechanical energy
180. Which of the following is scalar:
181. Which one is not present in AC generator?
182. Which one of the following is not present in A.C. generator
183. Which one of the following produced first:
184. Which phenomenon of the following is produced first
185. Who invented commutator:
186. Work can be stored in an inductor as:
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?