Question 1 What does a pin holder contain to make the pins stick to it?
Question 2 Name few items in the homes which have magnets in them?
Question 3 A sticker can be stuck to the steel door of a refrigerator or almirahs. Explain why?
Question 4 Describe briefly a method of making a magnet?
Question 5 What are the various ways in which magnet can lose their magnetism?
Question 6 What are the proper ways of storing bar magnet when not in use?
Question 7 A heap of metal scrap in a factory contain objects made up copper, aluminium, iron, zinc, steel, nickel, cobalt and lead.How will you separate them?
Question 8 Why the doors of a refrigerator close tightly?
Making your own Magnet
The easiest way of making a magnet is by the stroking method. If we stroke an iron bar with one end (one pole) of a bar magnet repeatedly in the same direction, the iron bar becomes a magnet. Thus, we need two things to make a magnet: an iron bar (or an iron strip) and a bar magnet.
Take an iron bar (or an iron strip) which is to be made a magnet and keep it on a wooden table. Also take a bar magnet. Hold one end of the bar magnet in your hand and keep the other end of bar magnet at one end of the iron bar. Without lifting, move the lower end
of bar magnet along the whole length of iron bar till you reach its other end. After reaching end , lift the bar magnet and bring its same end again at the starting end of the iron bar. Move the bar magnet again along the whole length of iron bar in the same direction.
Repeat this process of stroking the iron bar with the same end of bar magnet in the same direction about 30 to 40 times. The iron bar will then become a magnet.
The magnetic pole produced in iron bar at that end ‘where the stroke ends’ is always opposite of the stroking pole of the bar magnet.
We can even convert an iron nail, a sewing needle or even a razor blade into a magnet by stroking them repeatedly with the same end of a bar magnet in the same direction.If we convert an iron (or steel) needle into a magnet, then we can use this ‘magnetised needle’, for making our own compass.
Magnets can also be made by using electricity. The magnets made by using electricity are called electromagnets. Electromagnets are very useful because their magnetism (power of attraction) can be switched on’ or ‘off as desired. If the electric current is switched on through its coil, the electromagnet gets its magnetism (and starts behaving as a magnet). When the electric current through its coil is switched off, the electromagnet loses all its magnetism (and no longer behaves as a magnet).
Precautions in Handling Magnets
The magnets lose their property of magnetism if they are heated strongly, hit with a hammer or dropped from a height.
It is a common observation that science teachers get annoyed when students drop magnets on the floor. This is because dropping magnets from a height on the floor can destroy the magnetism of the magnets totally or partially and make them useless.
(1) We should never heat a magnet over a burner.
(2) We should never hit a magnet with a hammer.
(3) We should never drop a magnet on the floor.
(4) We should store the magnets properly (when not in use).
How to Store Magnets Properly
The magnets tend to lose their magnetism gradually and become weak over a period of time if they are not stored properly. To prevent the loss of magnetism, the magnets should be stored properly when not in use. This is done as follows.
(1) The bar magnets are stored in pairs (separated by a piece of wood) with their unlike poles on the same side and bars of soft iron kept across their ends.The first bar magnet has its N-pole on left side whereas the second bar magnet has its S-pole (unlike pole) on the left side. The soft iron bars kept across the ends of two bar magnets are called keepers (because they keep the magnetism of bar magnets safe) .
(2) The horseshoe magnets(U-shaped magnets) are stored properly just by keeping a bar of soft iron across their ends.
Uses of Magnets
Some of the important uses of magnets are given below :
(1) Magnets are used to hold objects (like stickers, refrigerator doors, pencil box lids, pins, etc).
(2) Magnets are used to separate discarded iron and steel objects from other waste (non- magnetic) materials.
(3) Magnets are used for making compasses.
(4) Magnets are used in telephones, hair driers, door bells, mixer and grinder, fans, washing machines, television sets, tape recorders, electric motors, electric generators and various types of toys.
Uses of magnet in Everyday Life
(1) We have all seen stickers that can be attached to iron and steel objects such as refrigerators and almirahs doors. Such stickers have flat magnets or button magnets below them. These magnets stick to the steel door of a refrigerator or almirahs and hold the sticker. Thus, magnets are used in stickers to hold them on to steel doors of refrigerators and almirahs.
2) The door of a refrigerator remains tightly closed. This is also due to the use of magnets, If we open the door of a refrigerator and look at it carefully, we will see a lining of rubber all around it. Inside this rubber lining is a long and thin strip of magnet. The thin strip of magnet in the door of a refrigerator attracts the steel body of refrigerator and keeps it closed tightly. Magnet is used in refrigerator door to keep it tightly closed.
(3) There are some pencil boxes made of plastic in which the lid shuts tightly when we close it. The box part of such a pencil box has a magnet in it whereas the lid has a strip of steel.When we close the lid of pencil box, the magnet pulls the strip of steel and holds the lid tightly. Thus, magnets are used in some pencil boxes to keep their lids shut tightly.
(4) The pin holders which are used in homes and offices have a magnet at their centre which attracts the steel pins and keeps them sticking to it. Thus, magnets are used in pin holders to keep the pins together.
(5) Magnets are also used in door-stoppers in homes and offices to hold the door open.
Everyday we throw away many old and useless objects made of iron and steel along with other waste materials of our household. These old and discarded iron and steel objects can be re-used (or recycled) by factories to make new things. Magnets are used to separate iron and steel objects from other waste materials.
An electromagnet is fitted to the long arm of a crane by chains. This long arm of crane is lowered over the heap of waste materials and electric current through the electromagnet is switched on. The old iron and steel objects present in the heap of waste materials get attracted by the electromagnet and hence stick to it. The arm of crane with iron and steel objects sticking to the electromagnet is now lifted up and the crane is moved to another place where the iron and steel objects are to be dropped. To drop the iron and steel objects
sticking to the electromagnet, the electric current passing through the electromagnet is switched off. When electric current is switched off, the electromagnet loses its magnetism (it no longer remains a magnet) and hence the iron and steel objects get detached from it. This process is repeated till all the old iron and steel objects present in the heap of waste materials are separated.The metal objects made of aluminium, copper, brass, etc., however, are not attracted by the magnet and hence remain behind in the heap of waste materials.
|Notes for Chapter 13 Fun with Magnets|