Magnetism Notes 6th Science Lesson 13 Notes in English

6th Science Lesson 13 Notes in English

13] Magnetism

Discovery of Magnets

• People wondered about this incident, each and everyone expressed their views.
• What might be the reason for the stick, to get stuck on the rock?
• Yes, you are right. That is a magnetic rock. People found it attracting not only for the stick of Magnus, but also for all the materials made of iron.
• The more rocks of these kinds were found worldwide.
• These magnetic rocks were named ‘Magnets’ and the ore is called as ‘Magnetite’ after the name of the boy Magnus.
• The name is also supposed to come after the name of the place (Magnesia) in which it was found.
• Magnetite was the ore with attracting property found in that region. Magnetites are natural magnets. They are called magnetic stones.
• Natural magnets do not have a definite shape.
• Since, they are used for finding direction, they are also called ‘leading stones’ or ‘lode stones’.

Magnet of different shapes

• After learning the method of changing the piece of iron into magnet (magnetization) we have been making and using several kinds of magnets.
• Such man-made magnets are called artificial magnets.
• Bar-magnet, Horseshoe magnet, Ring magnet and Needle magnet are generally used artificial magnets
• Oval-shape, Disc shapes Cylindrical and magnets are also available.

Magnetic and Non Magnetic Materials

• Substances which are attracted by magnet are called magnetic substances. Iron, cobalt, nickel are magnetic substances.
• Substances which are not attracted by magnet are called non-magnetic substances. Paper, plastic are called non- magnetic substances.

Magnetic Poles

• Place some iron filings on a paper. Place a bar magnet horizontally in the filings and turn it over a few times.
• Now lift the magnet.
• What do you see?
• Which part of the magnet has more iron filings sticking to it?
• Which part of the magnet has almost no filings sticking to it?
• The parts of the magnet those attract the largest amount of iron filings are called as its poles.
• The attractive force of the magnet is very large near the two ends. These two ends are called its poles.
• If you have a horseshoe magnet, or any other type of magnet at home, find the position of its poles by this experiment.
• In experiments with magnets you will need to use iron filings again and again.
• You can do this by placing a magnet in a pile of sand and turning it around in the sand.
• The small pieces of iron present in the sand will stick to the magnet. If you cannot find sand you can look for iron pieces in clayey soil as well.
• If you don’t have iron filings, you can collect small pieces of iron and they will serve the purpose as well.

Finding directions with a magnet

• Tie a piece of thread to the centre of a bar magnet and suspend it. Note, in which direction the magnet stops.
• Draw a line on a sheet of cardboard or the table along the direction in which the bar magnet stops
• This is roughly the north-south direction. The end of the magnet that points to the north is called the North Pole.
• The end that points to the south is called the South Pole.
• A freely suspended magnet always comes to rest in north-south direction.
• The directive property of magnets has been used for centuries to find directions.
• Around 800 years ago, the Chinese discovered that a suspended lode stone stops in the north-south direction.
• Chinese used these lode stones to find directions.
• The navigators of that country used to keep a piece of lode stone suspended in their boats and during a storm or mist, they used the lode stone to locate directions.

Magnetic compass

• A compass is an instrument which is used to find directions.
• It is mostly used in ships and airplanes.
• As a rule, mountaineers also carry a compass with them so that they do not lose their way in unknown places.
• The compass has a magnetic needle that can rotate easily. The marked end of the needle is the North Pole of the magnet.
• Can you use magnetic compass to find west direction?
• Ask your teacher to help you in using magnetic compass.

Properties of Magnets

Attraction or Repulsion

• Take two similar magnets, place them in four different ways as shown in Figure.
• Do magnets lose their properties? When?
• Magnets lose their properties if they are heated or dropped from a height or hit with a hammer.
• Magnets lose their properties when they are placed near Cellphone, Computer, DVDs. These objects will also get affected by magnetic field.

Storage of Magnets

• Improper storage can also cause magnets to lose their properties.
• To keep them safe, bar magnets should be kept in pairs with their unlike poles on the same side.
• They must be separated by a piece of wood and two pieces of soft iron should be placed across their ends.

• For a horse-shoe magnet a single piece of soft iron can be used as a magnetic keeper across the poles.

Usage of Magnets

• We use various equipment with magnets in day to day life.
• Discuss with your friends about the usage of the magnets in the following instances.

Science Today – Bullet Trains

• We know that like poles of the magnets repel each other.
• keep two Bar magnets as shown in figure.
• By using repulsion we can levitate a magnetic object. Let us make a toy and enjoy magnetic levitation.

How does the electromagnetic train work?

• Electromagnets are used in Electromagnetic train.
• Electromagnets are magnetised only when current flows through them.
• When the direction of current is changed the poles of the electromagnets are also changed.
• Like poles of the magnets which are attached at the bottom of the train and rail track repel each other. So, the train is lifted from the track up to a height of 10 cm.
• We know that we can move any magnetic object with the force of attraction or repulsion properties of magnets.
• This train also moves with the help of the magnets attached on the sides of track and the magnets fitted at the bottom sideway of the train.
• By controlling the current we can control the magnets and movement of the train.
• As there are no moving parts, there is no friction. So, the train can easily attain a speed of 300 km per hour. These trains are capable of running up to 600 km/ hour.
• They do not make any noise.
• They require less energy and they are eco-friendly.
• Even though, many countries have taken effort to use these trains, such trains are used for public transport only in China, Japan and South Korea.
• In India the possibilities of introducing these trains are under consideration.