Question:

A magnetising field of $1500\, A\, m^{-1}$ produces flux of $2.4 \times 10^{-5}$ weber in a iron bar of the cross-sectional area of $0.5 \,cm^2$. The permeability of the iron bar is

Updated On: Jun 23, 2023
  • $245$
  • $250$
  • $252$
  • $255$
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The Correct Option is D

Solution and Explanation

Here, $H = 1500\,A\,m^{-1}, \phi = 2.4 \times 10^{-5}$ weber $A = 0.5\, cm^{2} = 0.5 \times 10^{-4} \,m^{2}$ $\therefore\quad B = \frac{\phi}{A} = \frac{2.4 \times 10^{-5}}{0.5 \times 10^{-4}}$ $ = 4.8 \times 10^{-1}\,T$ and $\mu = \frac{B}{H} $ $= \frac{4.8 \times 10^{-1}}{1500} = 3.2 \times 10^{-4}$ So relative permeability $\mu_{r} = \frac{\mu}{\mu_{0}} = \frac{3.2 \times 10^{-4}}{4 \pi \times 10^{-7}}$ $ = 0.255 \times 10^{3} = 255$
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Notes on Magnetism and matter

Concepts Used:

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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.