GSEB Solutions for Class 7 Science and Technology – Properties of Magnet (English Medium)
The figure is a magnetic compass.
A needle type magnet is used in a magnetic compass.
The N_E_S_W written on the dial of a magnetic compass represents the directions. N stands for the North, E for East , S for the South and W for West.
The geographic North Pole is upwards on the sphere of the Earth.
The Earth behaves like a magnet. The magnetic South Pole of the Earth is near its geographic North Pole and the magnetic North Pole of the Earth is near its geographic South Pole.
We know that unlike poles attract each other.
So, when a magnet is suspended freely, its North Pole gets attracted towards the magnetic South Pole of the Earth. Similarly, the magnetic North Pole of the Earth attracts the South Pole of the freely suspended magnet.
As a result, the North Pole of the magnet becomes steady in the direction of the magnetic South Pole, that is, in the north direction of the Earth. Similarly the south pole of the magnet becomes steady in the direction of the magnetic North Pole, that is, in the south direction of the Earth. Thus, a freely suspended magnet always becomes steady in the north-south direction under the effect of the magnetic field of the Earth.
The geographic South Pole is downwards on the sphere of the Earth.
The magnetic south pole of the Earth is near its geographic North Pole.
The magnetic north pole of the Earth is near its geographic South Pole.
When we spread iron filings around a magnet, the iron filings arrange themselves in curved lines in a definite pattern. The lines around which the iron filings align themselves represent the magnetic field lines.
The following is the image of the magnetic field lines around the magnet:
The magnetic field lines are closely spaced at both the poles of the magnet. In other words, a strong magnetic field is found near poles of a magnet.
The bigger magnet will attract the iron pins from a closer distance as compared to the smaller magnet. This is because both the magnets have different magnetic field of lines. The bigger magnet will have more magnetic fields of lines.
In the magnet, the domains are arranged systematically in one direction. Whereas, in the iron piece the domains are oriented in random directions.
Yes, we can convert an iron needle into a magnet. This can be done by rubbing the needle with a magnet in one particular direction for some time.
An iron needle has domains that are arranged in random directions. But, when a magnet is rubbed in one direction, all the domains of the iron needle align themselves in one direction. So, the iron needle gets converted into a magnet.
When an iron nail is electro magnetised it acquires the property of a magnet and behaves like a magnet. Hence pins get attracted towards it.
When electric current (DC) is passes through an insulated copper wire wrapped around the nail, electromagnetic field is induced. This produces magnetism in the nail and it behaves like a magnet.
When any one end of the copper wire connected to the cell is disconnected, the pins attracted by the nail fall down. The iron nail can no longer attract the pins. This is because the magnetism is induced in the nail till the electric current passes through the insulated copper wire wrapped around the nail. As we disconnect any one end of the copper wire from the cell, the circuit breaks and the flow of electric current stops. Thus, the nails losses its magnetism and the nails fall down.
- Washing machine: Magnets are used in the lids of washing machines which touch its wall. This helps in closing the lid tightly.
- Refrigerator: Magnets are fitted in the doors of a refrigerator where it touches its walls.
- Tape recorder: Sound is recorded in the tape in the form of magnetic notation. When the tape recorder is played, we hear sound which was pre-recorded.
- Chappals with magnets: There are special chappals that have tiny magnets fitted in its sole.
- Crane: Strong electromagnets in cranes are used to lift heavy loads.
- Microphone: In microphones there is a strong magnet in its loudspeakers.
- The magnet is beaten over a hard object.
- The magnet is hammered.
- The magnets are arranged such that their like poles are placed side by side.
- The magnet is heated.
A magnet can lose its magnetism if it is dropped or hammered enough to disorganise its domains. Heating a magnet over a particular point will demagnetise it. Also, two magnets should not be arranged such that their like poles are positioned side by side.
There are many household items which we use in our day to day life where magnets are used.
Magnets are used in screw drivers, key chains and magnetic toys. In many appliances like washing machine, refrigerator, speakers, tape recorders, telephones and televisions, magnets are important components. Magnets are also used in electric motors, electric bells and electric fans. There are magnetic belts used for magnet therapy or magneto therapy. The stickers which we stick on the refrigerator and cupboard are also magnetic. Magnets are fitted to doors to make the door stick to the walls.
Let us consider a needle. Place it on a table and assume its ends to be as AB. Take a powerful bar magnet and place its North Pole near the end A of the needle as shown in the given image.
Rub the magnet with pressure on the needle from end A to end B. At point B, lift the magnet and bring it towards the point A as shown in the figure by the dotted line. Repeat the same process for several times. This will convert the needle into a magnet.
Take an iron nail. Take a long insulated copper wire and wound it around the nail as shown in the given image.
Connect the free ends of the wire to a cell. This allows electric current to flow through the wire wound around the nail. During this, bring some pins close to the iron nail. The iron nail will attract the pins and behave as a magnet. Thus we can say that the nail is electro magnetised.