2 Answers

To protect a material from the influence of an external magnetic field…

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To protect a material from the influence of an external magnetic field, the material should be kept in a

A. soft iron ring.

B. loop of copper wire.

C. triangular zinc ring.

D. square steel ring.




Most times, there arises need to shield materials such as electronics from external influence of nearby magnetic fields, this is because these fields could induce unwanted tiny currents that could alter circuit balance and functionality.

To perform a shield, a ferromagnetic metal or alloy is used to redirect the lines of flux of these magnetic fields, offering a kind of protection to the intended material.

Please note that the material mostly used to redirect magnetic lines of flux and offer shielding is steel, this is because of its cheap cost, availability and effectiveness.

Now for the right answer to the above question:

  1. Option A is incorrect. soft iron may not offer effective better shielding over a longer period of time because it is very easily magnetized.
  2. Option B is incorrect. current will be induced in the loop of copper wire; this current may induce its own fields that could attack the material intended to be protected.
  3. C is incorrect. zinc isn’t ferromagnetic, and so cannot effectively offer good shielding.
  4. D is the correct answer. Steel is the most commonly used material for this purpose.


You may please note these/this:

  • Although spherical shields are recommended, the shape of the shield does not matter much, instead the ferromagnetic nature of the substance is essential to offer effective redirection and protection.
  • Ferromagnetic materials like steel, cobalt, and nickel are good materials that could offer effective protection.
  • Although soft iron is also ferromagnetic, they are easily magnetized, this means they could themselves easily be turned into magnets, becoming the very threat they are expected to offer protection from.

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/ culled from 2016 JAMB-UTME physics past question 15 /

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