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Magnetics question

2023 · 11 Apr · Shift 2 · Q45
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Magnetics question

2023 · 11 Apr · Shift 2 · Q45

JEE MainPhysicsMagneticsMCQ+4 / −1
An electron is allowed to move with constant velocity along the axis of current carrying straight solenoid. A. The electron will experience magnetic force along the axis of the solenoid. B. The electron will not experience magnetic force. C. The electron will continue to move along the axis of the solenoid. D. The electron will be accelerated along the axis of the solenoid. E. The electron will follow parabolic path-inside the solenoid. Choose the correct answer from the options given below:
  1. A
    B, C and D only
  2. B
    B and C only
  3. C
    A and D only
  4. D
    B and E only
View written solutionFree

Correct answer: B

  1. Magnetic field inside a straight solenoid

    Along the axis of a current-carrying straight solenoid, the magnetic field is directed along the axis of the solenoid.

    So, if the electron moves along the axis, then its velocity v⃗\vec vv is parallel (or antiparallel) to the magnetic field B⃗\vec BB.

  2. Magnetic force on a moving charge

    The magnetic force on a charge is given by

    F⃗=q(v⃗×B⃗).\vec F = q(\vec v \times \vec B).F=q(v×B).

    If v⃗∥B⃗\vec v \parallel \vec Bv∥B, then

    v⃗×B⃗=0.\vec v \times \vec B = 0.v×B=0.

    Hence,

    F⃗=0.\vec F = 0.F=0.

    Therefore, the electron does not experience any magnetic force.

  3. Check each statement

    • A. The electron will experience magnetic force along the axis of the solenoid.
      False, because magnetic force is zero.

    • B. The electron will not experience magnetic force.
      True.

    • C. The electron will continue to move along the axis of the solenoid.
      True, since no magnetic force acts on it, so its motion remains unchanged.

    • D. The electron will be accelerated along the axis of the solenoid.
      False, because magnetic force is zero and magnetic field alone cannot accelerate a charge along its own direction.

    • E. The electron will follow parabolic path inside the solenoid.
      False, because no force acts, so the path remains straight.

  4. Correct combination

    The correct statements are B and C only.

    Hence the correct option is:

    Option B\boxed{\text{Option B}}Option B​
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