Question:

A wire carrying current $ I $ and other carrying $ 2I $ in the same direction produce a magnetic field B at the mid-point. What will be the field when $ 2I $ wire is switched off?

Updated On: Jun 23, 2023
  • B/2
  • 2B
  • B
  • 4B
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The Correct Option is C

Solution and Explanation

When currents in both the wries are in same direction, then magnetic field at the centre $B =B_{2}-B_{1}$ $=\frac{\mu_{0}(2 I)}{2 \pi(r / 2)}-\frac{\mu_{0} I}{2 \pi(r / 2)}$ $=\frac{\mu_{0} I}{\pi r}$ When $2 I$ wire is switched off, then magnetic field at the centre $B'=\frac{\mu_{0} I}{2 \pi(r / 2)}$ $=\frac{\mu_{0} I}{\pi r}=B$
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Notes on Magnetism and matter

Concepts Used:

Magnetism & Matter

Magnets are used in many devices like electric bells, telephones, radio, loudspeakers, motors, fans, screwdrivers, lifting heavy iron loads, super-fast trains, especially in foreign countries, refrigerators, etc.

Magnetite is the world’s first magnet. This is also called a natural magnet.  Though magnets occur naturally, we can also impart magnetic properties to a substance. It would be an artificial magnet in that case.

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Some of the properties of the magnetic field lines are:

  • The lines and continuous and outside the magnet, the field lines originate from the North pole and terminate at the South pole
  • They form closed loops traversing inside the magnet. 
  • But here the lines seem to originate from the South pole and terminate at the North pole to form closed loops.
  • More number of close lines indicate a stronger magnetic field
  • The lines do not intersect each other
  • The tangent drawn at the field line gives the direction of the field at that point.