Magnetic and non-magnetic materials

Do magnets stick to everything?

Do magnets stick only to objects made of certain materials? In Activity 4.1, you collect objects made of different materials, such as a pencil, an eraser, a key, a nail, a plastic scale, a glass bottle and a paper clip. First you predict which ones will stick to a magnet, then you bring a magnet near each one and observe, recording both in Table 4.1.

Magnetic materials

Some objects stick to the magnet. Materials that are attracted towards a magnet are called magnetic materials.

• Iron is a magnetic material. Most steel objects, such as pins, paper clips and nails, are attracted too, because steel is mostly iron.
• Nickel and cobalt are other metals that are also magnetic.
• Some combinations (mixtures) of these metals with other metals are also attracted towards magnets.

Extra: some stainless steel spoons and utensils are only weakly attracted or not at all, because of the other metals mixed in, so test before you predict.

Non-magnetic materials

Materials that are not attracted towards a magnet are called non-magnetic materials. Wood (pencil), rubber (eraser), plastic, glass, paper and cloth are non-magnetic. Many metals are non-magnetic too: aluminium, copper and brass are not attracted. So you cannot say that a magnet attracts all metals.

Sample Table 4.1

Object	Material	Attracted?
Pencil	Wood	No
Eraser	Rubber	No
Nail	Iron	Yes
Paper clip	Steel	Yes
Scale	Plastic	No
Bottle	Glass	No
Wire	Copper	No

Why sort materials with a magnet?

Knowing which materials are magnetic is useful. A magnet can quickly pick up pins or needles spilt on the floor. Extra: in scrap yards and recycling plants, large magnets separate iron and steel from other waste such as plastic, glass and aluminium. A magnet can also tell you whether a metal object contains iron: if a ‘metal’ spoon is not attracted, it may be made of aluminium or a kind of stainless steel. Remember that a magnet pulls hardest at its poles, so bring an end of the magnet, not its middle, near the object you are testing.

Magnetism through non-magnetic materials

What if a sheet of some material is placed between a magnet and a compass needle? In Activity 4.7, a magnet first deflects a compass needle. Then, without moving them, a piece of wood is placed between them, followed by cardboard, a thin plastic sheet and a thin glass sheet.

There is no appreciable change in the needle’s deflection. We conclude that the magnetic effect can act through non-magnetic materials.

Fun uses of this idea

• Steel balls in a maze: move a magnet under the cardboard tray and the balls follow it through the maze.
• A paper clip in water: hold a magnet against the outside of the glass and slide it up; the clip follows, and neither your fingers nor the magnet get wet.
• A garland: hang steel pins one below another from a magnet; each pin attracts the next.

Magnets can move some objects without touching them. To find where a magnet pulls hardest, read poles of a magnet. For the textbook’s questions, see the Chapter 4 NCERT solutions; for the whole chapter, see the Chapter 4 notes.