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12th Grade > Physics

ELECTROMAGNETIC WAVES AND INDUCTION MCQs

Electromagnetic Waves, Electromagnetic Induction, Waves On A String

Total Questions : 73 | Page 1 of 8 pages
Question 1. If in a coil rate of change of area is  5metre2millisecond and current become 1 amp form 2 amp in 2× 103 sec. If magnetic field is 1 Tesla then self inductance of the coil is
  1.    2 H
  2.    5 H
  3.    20 H
  4.    10 H
 Discuss Question
Answer: Option D. -> 10 H
:
D
e=B.dAdt=Ldidt1×5103=L×(21)2×103L=10H
Question 2. Television signals broadcast from the moon can be received on the earth while the TV broadcast from Delhi cannot be received at places about 100 km distant from Delhi. This is because
  1.    There is no atmosphere around the moon
  2.    Of strong gravity effect on TV signals
  3.    TV signals travel straight and cannot follow the curvature of the earth
  4.    There is atmosphere around the earth
 Discuss Question
Answer: Option C. -> TV signals travel straight and cannot follow the curvature of the earth
:
C
Over a long distance, earths’ surface will be curved and since TV signals travel in straight line television broad cast signals cannot be received.
Question 3. The magnetic field in the cylindrical region shown in figure increases at a constant rate of 20 mT/sec. Each side of the square loop ABCD has a length of 1 cm and resistance of 16 ohm. Find the current in the wire AB if the switch S is closed
The Magnetic Field In The Cylindrical Region Shown In Figure...
  1.    1.25× 10−7A ,(anti-clockwise)
  2.    1.25× 10−7A ,(clockwise)
  3.    2.5× 10−7A ,(anti clockwise)
  4.    2.5× 10−7A ,(clockwise)
 Discuss Question
Answer: Option A. -> 1.25× 10−7A ,(anti-clockwise)
:
A
i=eR=AR.dBdt=(1×102)216×20×103=1.25×107 A
(Anti-clockwise).
Question 4. A hundred turns of insulated copper wire are wrapped around an iron cylinder of area 103 m2 and are connected to a resistor. The total resistance in the circuit is 10 ohms. If the longitudinal magnetic induction in the iron changes from 1 weber m2, in one direction to 1 Weber m2 in  the opposite direction, how much charge flows through the circuit?
  1.    2× 10−2C
  2.    2× 10−3C
  3.    2× 10−4C
  4.    2× 10−5C
 Discuss Question
Answer: Option A. -> 2× 10−2C
:
A
dQ=dϕR=nAdBR=100×1×103×210=2×102C
Question 5. A pair of parallel conducting rails lie at right angle to a uniform magnetic field of 2.0 T as shown in the fig. Two resistors  10Ω  and 5Ω are to slide without friction along the rail. The distance between the conducting rails is 0.1 m. Then 
A Pair Of Parallel Conducting Rails Lie At Right Angle To A ...
  1.    Induced current = 1150A directed clockwise if 10Ω resistor is pulled to the right with speed 0.5ms−1 and 5Ω resistor is held fixed
  2.    Induced current = 1300A directed anti-clockwise if 10Ω resistor is pulled to the right with speed 0.5ms−1 and 5Ω resistor is held fixed
  3.    Induced current = 1300A directed clockwise if 5Ω resistor is pulled to the left at speed 0.5ms−1 and 10Ω resistor is held at rest
  4.    Induced current =1150A directed anti-clockwise if 5Ω resistor is pulled to the left with speed 0.5ms−1 and 10Ω resistor is held at rest
 Discuss Question
Answer: Option D. -> Induced current =1150A directed anti-clockwise if 5Ω resistor is pulled to the left with speed 0.5ms−1 and 10Ω resistor is held at rest
:
D
When 5Ω resistor is pulled left at 0.5 m/sec induced emf., in the said resistor
=e=vBl=0.5×2×0.1=0.1V
Resistor 10Ω is at rest so induced emf in it (e=vBl) be zero.
Now net emf., in the circuit=0.1V and Equivalent resistance of the circuit
R=15Ω
A Pair Of Parallel Conducting Rails Lie At Right Angle To A ...
Hence current i=0.115 amp=1150amp
And its direction will be anti-clockwise (according to Lenz's law)
Question 6. A coil of wire having finite inductance and resistance has a conducting ring placed coaxially within it. The coil is connected to a battery at time t = 0, so that a time-dependent current starts flowing through the coil. If I1 is the current induced in the ring, and B is the magnetic field at the axis of the coil due to I2, then as a function of time (t> 0), the product I2 (t) B(t)
  1.    Increases with time
  2.    Decreases with time
  3.    Does not vary with time
  4.    Passes through a maximum 
 Discuss Question
Answer: Option D. -> Passes through a maximum 
:
D
Using k1,k2 etc, as different constants.
I1(t)=k1[1etτ],B(t)=k2I1(t)
I2(t)=k3dB(t)dt=k4etτ
l2(t)B(t)=k5[1etτ][etτ]
This quantity is zero for t=0and t= and positive for other value of t. It must , therefore, pass through a maximum.
Question 7. An aircraft with a wing-span of 40 m flies with a speed of 1080 km h1 in the eastward direction at a constant altitude in the northern hemisphere, where the vertical component of earth's magnetic field is 1.75 ´ 105T. Then the emf that develops between the tips of the wings is
  1.    0.5 V
  2.    0.35 V
  3.    0.21 V
  4.    2.1 V
 Discuss Question
Answer: Option C. -> 0.21 V
:
C
L=40 m, v=1080km h1=300msec1 and B=1.75×105T
e=Blv=1.75×105×40×300=0.21V
Question 8. The intensity of gamma radiation from a given source is I. On passing through  36 mm of lead, it is reduced to I8. The thickness of lead which will reduce the intensity to l2 will be
  1.    18 mm
  2.    12 mm
  3.    6 mm
  4.    9 mm
 Discuss Question
Answer: Option B. -> 12 mm
:
B
I=Ieμxx=1μlogeII (where l= original intensity, I'= changed intensity)
36=1μlogeII8=3μloge2 ......(i)
x=1μlogeII2=1μloge2 ......(ii)
From equation (i) and (ii), x=12mm.
Question 9. Which of the following radiations has the least wavelength
  1.    γ -rays
  2.    β-rays
  3.    α-rays
  4.    X-rays
 Discuss Question
Answer: Option A. -> γ -rays
:
A
λYrays<λXrays<λαrays<λβrays
Question 10. What are non-mechanical waves?
  1.    Waves that travel in such a way that wave direction is perpendicular to motion of particles
  2.    Waves that travel in such a way that wave direction is same as motion of particle
  3.    Those which do not require material medium to travel
  4.    Those that require material medium to travel.
 Discuss Question
Answer: Option C. -> Those which do not require material medium to travel
:
C
Non-Mechanical waves are waves that do not require a material medium to travel. . For example light from starstravels through space to earth.

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