JEE Main PYQs on Electric and Magnetic Fields: JEE Main Questions for Practice with Solutions

JEE Main Questions

• 1.

  Let \( B_1 \) be the magnitude of magnetic field at the center of a circular coil of radius \( R \) carrying current \( I \). Let \( B_2 \) be the magnitude of magnetic field at an axial distance \( x \) from the center. For \( x : R = 3 : 4 \), \( \frac{B_2}{B_1} \) is:

  • 4 : 5
  • 16 : 25
  • 64 : 125
  • 25 : 16
    
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• 2.

  A proton is moving undeflected in a region of crossed electric and magnetic fields at a constant speed of \( 2 \times 10^5 \, \text{m/s} \). When the electric field is switched off, the proton moves along a circular path of radius 2 cm. The magnitude of electric field is \( x \times 10^4 \, \text{N/C} \). The value of \( x \) is \_\_\_\_\_. (Take the mass of the proton as \( 1.6 \times 10^{-27} \, \text{kg} \)).

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• 3.

  Given below are two statements. One is labelled as Assertion (A) and the other is labelled as Reason (R).
  Assertion (A): A magnetic monopole does not exist.
  Reason (R): Magnetic lines are continuous and form closed loops.
  In the light of the above statements, choose the correct answer from the options below:

  • (A) is false but (R) is true
    
  • (A) is true but (R) is false
    
  • Both (A) and (R) are true but (R) is NOT the correct explanation of (A)
    
  • Both (A) and (R) are true and (R) is the correct explanation of (A)
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• 4.

  Uniform magnetic fields of different strengths $ B_1 $ and $ B_2 $, both normal to the plane of the paper, exist as shown in the figure. A charged particle of mass $ m $ and charge $ q $, at the interface at an instant, moves into region 2 with velocity $ v $ and returns to the interface. It continues to move into region 1 and finally reaches the interface. What is the displacement of the particle during this movement along the interface?
  
  Consider the velocity of the particle to be normal to the magnetic field and  $ B_2 > B_1 $.

  • \( \frac{mv}{qB_1} \left( 1 - \frac{B_2}{B_1} \right) \times 2 \)
  • \( \frac{mv}{qB_1} \left( 1 - \frac{B_1}{B_2} \right) \)
  • \( \frac{mv}{qB_1} \left( 1 - \frac{B_2}{B_1} \right) \)
  • \( \frac{mv}{qB_1} \left( 1 - \frac{B_1}{B_2} \right) \times 2 \)
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• 5.

  The figure shows a circular portion of radius \( \frac{R}{2} \) removed from a disc of mass \( m \) and radius \( R \). The moment of inertia about an axis passing through the centre of mass of the disc and perpendicular to the plane is:

  • \( \frac{13}{32} mR^2 \)
    
  • \( \frac{mR^2}{2} \)
    
  • \( \frac{mR^2}{4} \)
    
  • \( \frac{13}{64} mR^2 \)
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• 6.

  A monochromatic light is incident on a metallic plate having work function \( \phi \). An electron, emitted normally to the plate from a point A with maximum kinetic energy, enters a constant magnetic field, perpendicular to the initial velocity of the electron. The electron passes through a curve and hits back the plate at a point B. The distance between A and B is:

  • \( \sqrt{\frac{2m \left( \frac{hc}{\lambda} - \phi \right)}{eB}} \)
  • \( \frac{m \left( \frac{hc}{\lambda} - \phi \right)}{eB} \)
  • \( \sqrt{8m \left( \frac{hc}{\lambda} - \phi \right)} \div eB \)
  • \( 2 \frac{m \left( \frac{hc}{\lambda} - \phi \right)}{eB} \)
    
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