SIMPLE PHENOMENA OF

MAGNETISM

1.Name some objects with magnets in themToys, fridge door, head phone ,speaker etc.2.During migration time some birds are able to navigate in the correct direction.How?

WARM UP

Students will be able to1.State the properties of magnets.2.Distinguish between ferrous and non-ferrous materials3.Distinguish between Magnetically hard and soft materials4.Define poles of a magnet.

LEARNING OBJECTIVES

History of magnetismAncient travellers used rocks with magnetic properties , known as lodestone to guide their journeys. Lodestone which is magnetic points towards north when freely suspended..

History of Magnetism

Magnetic polesThe two ends of the magnet where magnetism is strongest. Magnets attract magnetic substances like iron nickel cobalt

Earth is a huge magnet.

Earth behaves as if there is a huge bar magnet along its axis. The magnetic north of the earth points towards the geographic south and the magnetic south of the earth points towards the geographic north.

Properties of magnets 1. Magnets attract magnetic substances like iron,nickel,cobalt.2.The force of attraction of the magnet is greater at its poles than at the middle.3.Like poles of magnets repel and unlike poles attract.4.A freely suspended magnet will always point in the North- south direction

Alloys are combinations of different elements.

Magnetically hard Some alloys remain permanently magnetic once they are magnetized. Eg.steel. These are used to make permanent magnets.

Magnetically soft. These materials retain magnetism only temporarily .eg. Pure iron. These are used to make electromagnets and the relay

Magnetically hard and magnetically soft materials do not refer to their physical hardness or feel but to their magnetic behaviour. Ferrous alloys- Alloys which contain ironNon ferrous alloys-Alloys which do not contain ironIn the past all magnetic materials were ferrous. But this is no longer true. The strongest magnet samarium –cobalt is non ferrous.

Continous assessment1.What happens when a magnet is freely suspended?2.What happens when like poles are brought together? 3.What happens when a north seeking pole is brought near a south seeking pole?4.What are alloys?5.Which magnet is used in head phones?

Final assessment1.Define poles of a magnet.2. What happens when a magnet is freely suspended? Why?3.Name some magnetic substances.4.List the properties of magnets.5..Distinguish between ferrous and non-ferrous materials6.Distinguishbetween Magnetically hard and soft materials