Distinguish between diamagnetic, paramagnetic and ferromagnetic substances, with one example of each. Explain ferromagnetism using domains.
How to lay out the answer. Follow the frame, then write it in your own words.
1 · Open with the idea. Materials are classed by how they respond to a field: by the sign and size of χ.
2 · Compare in a table.
χ: small negative / small positive / very large.
μr: just below 1 / just above 1 / much greater than 1.
Non-uniform field: moves to weaker / to stronger / strongly to stronger.
3 · Give examples. Bismuth or copper; aluminium or oxygen; iron, cobalt or nickel.
4 · Explain domains. In a ferromagnet, atomic moments line up in domains; a field makes the aligned domains grow and the others turn, giving a large M.
5 · Draw domains. [Two boxes of domains with arrows: random with no field; mostly lined up along B with the field on]
6 · Real life. A fridge magnet sticks to a steel almirah but not to an aluminium kadai.
7 · Close in one line. So, χ < 0 for dia, small χ > 0 for para, and χ much greater than 1 for ferro.
Scoring tip: A neat three-column table scores best. Give the sign of χ in every column.
