Transcript d) 0 - rajendranmaster

12TH STANDARD
PHYSICS
Electro magnetic induction
and Alternating currents
Prepared by:
R.RAJENDRAN, M.A., M.Sc., M.Ed.,
N.INGARAN, M.Sc., M.Phil.,M.Ed.,
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01. Lenz law is in accordance with the law of
conservation of ………………………
a) momentum
b) energy
c) voltage
d) current
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02. The self inductance of a straight conductor is
……………………
a) infinity
b) zero
c) maximum
d) minimum
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03. The unit henry can also be written as ……………………
a) H
b) A
c) V s A-1
d) m / s
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04. Transformer works on ………………… currents only.
a) direct
b) alternating
c) both direct and alternating
d) steady
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05. The part of the AC generator that passes the current
from the coil to the external circuit is
a) armature
b) slip rings
c) field magnet
d) brushes
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06. The number of magnetic lines of forces crossing unit
area in a magnetic field is magnetic …………………
a) flux
b) induction
c) permeability
d) radiation
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07. Electromagnetic induction was discovered by
……………….
a) Lenz
b) Hertz
c) Michael Faraday
d) Oersted
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08. Fleming’s right hand rule is also called as …………………
rule.
a) cork screw
b) thumb
c) end
d) generator
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09. The unit of self inductance is …………………...
a) H
b) A
c) V s A-1
d) m / s
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10. The energy stored in an inductor is given by E =
……………….
a) ½ L2 Io
b) L Io2
c) L / Io2
d) ½ L Io2
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11. The equation for the mutual induction of two long
solenoids is M = ………………..
a) μo N1 N2 A / l
b) I / μo N1 N2 A
c) μo N1 N2 A2 / l
d) N1 N2 A / l
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12. The induced emf by changing the area enclosed by a
coil in a magnetic field is e = ……….
a) EoSinωt
b) – Blv
c) - Bil
d) – NBIA
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13. When the plane of a coil is perpendicular to a
magnetic field, the induced emf is ………….
a) maximum
b) minimum
c) zero
d) infinity
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14. AC generator is a device used for converting the
mechanical energy into ………..
a) sound energy
b) heat energy
c) electrical energy
d) light energy
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15. If a number armature coils are used in the alternator,
it is called as …………. Alternator.
a) single phase
b) two phase
c) three phase
d) poly phase
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16. Electro magnetic brakes use ……….. current .
a) direct
b) uni-directional
c) eddy
d) steady
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17. Transformer works on the ……………… principle.
a) electro static induction
b) Huygens’s
c) electromagnetic induction
d) self induction
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18. The ratio of the output power to the input power of a
transformer is called ………………
a) velocity ratio
b) mechanical advantage
c) power loss
d) efficiency
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19. Eddy current losses are minimized by using a core
made of ……………… an alloy of steel.
a) mumetal
b) stelloy
c) brass
d) nichrome
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20. The frequency of AC used for domestic power in India
is …………..
a) 0 Hz
b) 50 Hz
c) 100 Hz
d) 400 Hz
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21. The average value of the AC over one complete cycle
is …………..
a) 0
b) maximum
c) minimum
d) infinity
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22. The relation between Irms and Io is ………………
a) Irms = Io / √ 2
b) Irms = Io × √ 2
c) Irms = Io / 2
d) Irms = √ Io / 2
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23. In an AC circuit containing R only, the phase
difference between current and voltage is ……
a) 0
b) π / 2
c) π / 4
d) π
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24. The inductive reactance XL is given by XL = ……
a) L ω
b) 1 / L ω
c) L / ω
d) ω / L
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25. A capacitor offers infinite resistance to …………
current.
a) alternating
b) direct
c) varying
d) sinusoidal
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26. In RLC circuit, the instantaneous current is given by I
= ………………….
a) Io Sin ( ω t ± φ )
b) Io tan ( ω t ± φ )
c) Io cos ( ω t ± φ )
d) Io / √ 2
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27. The equation for Q factor is given by Q = …………..
a) 1 /2 π √ L /C )
b) R ( √ L /C )
c) 1 /R ( √ L /C )
d) 1 /R L C
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28. The average power consumed over a complete cycle
is Pav =
a) E rms I rms tan φ
b) E rms I rms sin φ
c) E rms I rms sec φ
d) E rms I rms cos φ
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29. Choke coil is used to control the current in an …………
circuit.
a) DC
b) AC
c) AC and DC
d) steady
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30. Choke coils are used in ………….. tubes which work on
alternating currents.
a) filament
b) oil
c) fluorescent
d) glass
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31. The reactance of an inductor is ………………
proportional to the frequency.
a) first directly, then inversely
b) first inversely, then directly
c) directly
d) inversely
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32. Shell type cores are used to minimize …………………
losses.
a) eddy current
b) power
c) hysteresis
d) flux
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33. The number of magnetic lines of forces crossing a
closed area is called magnetic ……………..
a) flux
b) induction
c) permeability
d) radiation
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34. The selectivity or sharpness of a resonant circuit is
measured by the …………… factor.
a) safety
b) power
c) quality
d) energy
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35. The ratio of the voltage across a coil or capacitor to
the applied voltage is called as …………factor.
a) safety
b) quality
c) power
d) energy
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36. For normal frequencies, the Q factor lies between
……………...
a) 1 and 10
b) 100 and 1000
c) 10 and 100
d) 0.1 and 10
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37. For radio frequencies, air chokes are used. These
chokes are called as ………… chokes.
a) AF
b) AF or RF
c) R F or H F
d) AF or HF
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38. Whenever there is a change in the magnetic flux
linked with a closed circuit, an emf is induced in it. This
phenomenon is called …………………..
a) electro static induction
b) action of points
c) electromagnetic induction
d) self induction
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39. In Fleming’s right hand rule, the middle finger points
the direction of the …………
a) motion of the conductor
b) magnetic field
c) induced current
d) force
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40. The property of the coil which enables to produce an
opposing induced emf in it when the current in the coil
changes is called ……………………
a) electro static induction
b) self induction
c) electromagnetic induction
d) induction
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41. If two coils are wound on a soft iron core one over
the other , the mutual induction is ………………
a) zero
b) infinity
c) minimum
d) very large
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42. The induced emf is given by the equation e =
……………
a) Eo sin ωt
b) Eo cosωt
c) Eo sec ωt
d) Eo tan ωt
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43. In fans, …………….. motors are used.
a) electro static induction
b) self induction
c) electromagnetic induction
d) induction
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44. In step up transformers, the transformer ratio k is
…………… than one.
a) lesser
b) greater
c) smaller
d) none
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45. A power of 11kW is transmitted at 5.5kV through a
transmission line of 1 ohm. The power loss = ………
a) 4 W
b) 40 W
c) 0.4 W
d) 400 W
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46. In an AC circuit containing C only, the phase
difference between the current and the voltage is
……………
a) 0
b) π / 2
c) π / 4
d) π
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47. In an LCR circuit, at resonance, the impedance is
…………….
a) minimum
b) maximum
c) infinity
d) zero
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48. The rms value of the AC is ………….. times the peak
value of the alternating current.
a) 1.414
b) 1.732
c) 0.707
d) 2.000
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49. The direction of the eddy current can be noted by
……………
a) Faraday’s laws
b) Lenz’s law
c) cork screw rule
d) end rule
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50. In a three phase AC generator, the emf’s of the coils
differ by ………………...
a) 120
b) 180
c) 90
d) 0
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51. Electromagnetic induction is not used in
(a) transformer
(b) room heater
(c) AC generator
(d) choke coil
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52. A coil of area of cross section 0.5 m2 with 10 turns is
in a plane which is penpendicular to an uniform
magnetic field of 0.2 Wb/m2. The flux though the coil
is
(a) 100 Wb
(b) 10 Wb
(c) 1 Wb
(d) zero
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53. Lenz’s law is in accordance with the law of
(a) conservation of charges
(b) conservation of flux
(c) conservation of momentum
(d) conservation of energy
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54. The self−inductance of a straight conductor is
(a) zero
(b) infinity
(c) very large
(d) very small
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55. The unit henry can also be written as
(a) Vs A−1
(b) Wb A−1
(c) Ω s
(d) all
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56. An emf of 12 V is induced when the current in the
coil changes at the rate of 40 A S–1. The coefficient of
self induction of the coil is
(a) 0.3 H
(b) 0.003 H
(c) 30 H
(d) 4.8 H
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57. A DC of 5A produces the same heating effect as an AC
of
(a) 50 A rms current
(b) 5 A peak current
(c) 5A rms current
(d) none of these
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58. Transformer works on
(a) AC only
(b) DC only
(c) both AC and DC
(d) AC more effectively than DC
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59. The part of the AC generator that passes the current
from the coil to the external circuit is
(a) field magnet
(b) split rings
(c) slip rings
(d) brushes
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60. In an AC circuit the applied emf e = Eo sin (ωt + π/2)
leads the current I = Io sin (ωt – π/2) by
(a) π/2
(b) π/4
(c) π
(d) 0
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61. Which of the following cannot be stepped up in a
transformer?
(a) input current
(b) input voltage
(c) input power
(d) all
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62. The power loss is less in transmission lines when
(a) voltage is less but current is more
(b) both voltage and current are more
(c) voltage is more but current is less
(d) both voltage and current are less
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63. Which of the following devices does not allow d.c. to
pass through?
(a) resistor
(b) capacitor
(c) inductor
(d) all the above
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64. In an ac circuit
(a) the average value of current is zero.
(b) the average value of square of current is zero.
(c) the average power dissipation is zero.
(d) the rms current is 2 time of peak current.
THE END