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Moving Charges and Magnetism — Physics STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 SciencePhysicsMoving Charges and Magnetism1 Mark
MCQ
Consider a wire carrying a steady current, I placed in a uniform magnetic field B perpendicular to its length. Consider the charges inside the wire. It is known that magnetic forces do no work. This implies that:
  • A
    Motion of charges inside the conductor is unaffected by B since they do not absorb energy.
  • B
    Some charges inside the wire move to the surface as a result of B.
  • C
    If the wire moves under the influence of B, no work is done by the force.
  • D
    If the wire moves under the influence of B, no work is done by the magnetic force on the ions, assumed fixed within the wire.
✓

Answer

  1. Some charges inside the wire move to the surface as a result of B.​​​​​​
  1. If the wire moves under the influence of B, no work is done by the magnetic force on the ions, assumed fixed within the wire.

Solution:

Magnetic force on a conductor of length l carrying a current I placed in a uniform magnetic field B is given by, $\text{F}=\text{I}(\text{l}\times\text{B})\text{ or }|\text{F}|=\text{I }|\text{l}| \ \ |\text{B}|\sin\theta$.

The direction of force is given by Fleming's left hand rule & F is perpendicular to the direction of magnetic field B, Therefore, work done by the magnetic force on the ions is zero.

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