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## ELECTROMAGNETIC INDUCTION Quiz-12

As per analysis for previous years, it has been observed that students preparing for NEET find Physics out of all the sections to be complex to handle and the majority of them are not able to comprehend the reason behind it. This problem arises especially because these aspirants appearing for the examination are more inclined to have a keen interest in Biology due to their medical background. Furthermore, sections such as Physics are dominantly based on theories, laws, numerical in comparison to a section of Biology which is more of fact-based, life sciences, and includes substantial explanations. By using the table given below, you easily and directly access to the topics and respective links of MCQs. Moreover, to make learning smooth and efficient, all the questions come with their supportive solutions to make utilization of time even more productive. Students will be covered for all their studies as the topics are available from basics to even the most advanced. .

Q1. If the current is halved in a coil, then the energy stored is how much times the previous value
•  1/2
•  1/4
•  2
•  4
Solution

Q2. A 50 mH coil carries a current of 2 A, the energy stored in joule is
•  1
•  0.05
•  10
•  0.1
Solution
Energy stored, U=1/2 Li2 = 1/2×50×10-3×2×2=0.1 J

Q3. A coil has an area of 0.05 m^2 and it has 800 turns. It is placed perpendicularly in a magnetic field of strength 4×10-5 Wb/m2, it is rotated through 90° in 0.1 sec. The average e.m.f. induced in the coil is
•  0.056 V
•  0.046 V
•  0.026 V
•  0.016 V
Solution

Q4. A cylindrical bar magnet is kept along the axis of a circular coil. The magnet is rotated about its axis such that north pole faces the coil. The induced current in the coil
•  Is zero
•  Is clock-wise from magnet side
•  May be clock-wise or anti clock wise
•  Is anti-clock-wise from magnet side
Solution
On rotating the magnet, no change in flux is linked with the coil. Therefore, induced emf/ current is zero.

Q5. A circular wire of radius r rotates about its own axis with angular speed Ï‰ in a magnetic field B perpendicular to its plane, then the induced emf is
•  1/2 BrÏ‰2
•  BrÏ‰2
•  2BrÏ‰2
•  Zero
Solution
The emf induces when there is change of flux. As in this case there is no change of flux, hence no emf will be induces in the wire

Q6. Which of the following phenomena is utilised in the construction of mouth piece of a telephone now a days?
•  Thermo electric effect
•  Photo electric effect
•  Change of resistance with pressure
•  Electromagnetic induction
Solution
In the construction of mouth piece of a telephone, we use the phenomenon of change of resistance with pressure (of sound waves).

Q7. A conducting rod AC of length 4l is rotated about a point O in a uniform magnetic field B ⃗ directed into the paper. AO=land OC=3l. Then

•  VA-VO=(BÏ‰l2)/2
•  VO-VC=7/2 BÏ‰l2
•  VA-VC=4 BÏ‰l2
•  VC-VO=9/2 BÏ‰l2
Solution
By using e=1/2 Bl2Ï‰
For part AO; eOA=eO-eA=1/2 Bl2Ï‰
For part OC; eOC=eO-eC=1/2 B(3l)2Ï‰
∴eA-eC=4 Bl2Ï‰

Q8. The north pole of a long horizontal bar magnet is being brought closer to a vertical conducting plane along the perpendicular direction. The direction of the induced current in the conducting plane will be
•  Horizontal
•  Vertical
•  Clockwise
•  Anticlockwise
Solution
According to Lenz’s law.

Q9. A varying current at the rate of 3 A/s in a coil generates an e.m.f. of 8 mV in a nearby coil. The mutual inductance of the two coils is
•  2.66 mH
•  2.66×10-3mH
•  2.66 H
•  0.266 H
Solution
|e|=M di/dt⇒8×10-3=M×3⇒M=2.66mH

Q10.  A magnet is made to oscillate with a particular frequency, passing through a coil as shown in figure. The time variation of the magnitude of e.m.f. generated across the coil during one cycle is

•

•

•

•

Solution
As the north pole approaches, a north pole is developed at the face, i.e., the current flows anticlockwise. Finally when it completes the oscillation, no emf is present. Now south pole approaches the other side, i.e., RHS, the current flows clockwise to repel the south pole. This means the current is anticlockwise at the LHS a before. The break occurs when the pendulum is at the extreme and momentarily stationary

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