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Railways PYQCBT 2 2017

RRB NTPC · Question 91

Which one is NOT true for electromagnets?

  1. It is a temporary magnet.

  2. Its strength varies with the air gap between its poles.

  3. Polarity cannot be changed.

  4. Its strength can be changed.

Show answer & explanation

Answer: (C) Polarity cannot be changed.

Explanation

An electromagnet is temporary and its strength can be changed. Its polarity can be reversed by reversing the direction of the current, so 'polarity cannot be changed' is not true.