An electromagnet used in a telegraph relay must switch on and off several times per second
PHYSICS · Single correct · CBSE · Physics · Magnetism and Matter · Magnetism and Matter
Problem
An electromagnet used in a telegraph relay must switch on and off several times per second. Which of the following best explains why its core is made of soft iron rather than hard steel?
(a) Soft iron has lower electrical resistivity than hard steel, so induced eddy currents in the core are smaller and the magnetic field can change more rapidly.
(b) Hard steel’s domains are already fully aligned, so it cannot significantly increase its magnetization when the current is switched on.
(c) Soft iron has high magnetic permeability but low remanence, so it magnetizes strongly while the current flows and loses most of its magnetization almost immediately when the current stops.
(d) Soft iron can reach a higher saturation magnetization than hard steel, so it produces a stronger field for a given current and therefore switches faster.