PHYSICS [5 Mark Question Answer]

The two ways of magnetising an iron piece are:
1. Magnetic induction method:
Take a long iron nail and test it for magnetic properties by bringing near the magnetic substances. You will see nail does not attract the magnetic substances. Now bring near a pole of a bar magnet to the head of the nail. Now bring the iron paper clips near the pointed end of the nail, you will observe that the iron paper clips now get attracted towards the nail. This is because the iron nail has become a magnet. Now take the bar magnet away from the iron nail, paper clips fall off. This magnetism is temporary.

2. Single touch method:
Take a demagnetised piece of iron. Place it on a stable surface. Take a magnet and select its one pole. Now MB it with the selected pole on the iron in one direction several times. After some time, the iron piece turns into a magnet.

Suspend a bar magnet with a silk thread from a wooden stand as shown in the figure. The magnet swings for some time and then eventually comes to rest in a particular direction i.e., north-south direction. If we disturb the magnet a little, the magnet again comes to rest in the north-south direction.

The end of the magnet which points towards the north is called the north-seeking pole or simply the north pole and the end which points towards the south is called the south seeking pole or simply the south pole. The north and south poles are marked by the letters N and S respectively.

1. Take two bar magnets A and B. Suspend one magnet A with a silk thread from support so that it is free to swing. The magnet will come to rest in the north-south direction. The north pole of the magnet is in the north direction and the south pole of the magnet is in the south direction.
2. Now holding the other magnet B in your hand, bring its north pole near the north pole of the suspended magnet A (such that the two magnets do not touch each other) as shown in the figure. You will observe that the suspended magnet A moves away from the magnet B. This shows that the like poles repel each other.

Now bring the south pole of the magnet B near the north pole of the suspended magnet A as shown in the figure, without touching it. You will observe that the magnet A moves towards the magnet B. This shows that the unlike poles attract each other.

Aim: To make an electromagnet.
Materials Required: An iron nail, a battery, a switch, some insulated copper wire, and some iron paper pins.
Procedure: Coil the insulated copper wire around the iron nail. Connect the ends of the wire to the battery through the switch. Close the switch so that electric current flows through the copper wire. Now bring the iron paper pins close to the iron nail.
Observation And Conclusion: The paper pins get attracted to the nail, showing that the nail has turned into an electromagnet. Now, if you switch off the current, the iron paper pins will drop off the iron nail.

The property by which an ordinary piece of iron acquires magnetic properties temporarily due to the presence of another magnet close to it is known as magnetic induction
Take a long nail. Put it on the arm of a stand. Spread some iron pins on the base of the stand. You will find that the pins do not get attracted to the nail. Now touch a magnet at the end of the nail. As the end is brought close to the head of the nail, some pins cling to the nail. It happens because the nail turns into the magnet and acquires the properties of magnetism. The moment you remove the magnet from the head of the nail. The pins will fall down. It will no more be a magnet.

The space around a magnet in which if a magnetic substance such as small pieces of iron are placed, they get attracted to the magnet, which is called the magnetic field.
Recognition of the magnetic field around a magnet: If a magnet is placed below a sheet of stiff paper and some iron filings are spread on it, then on tapping the sheet gently, the iron filings are found to arrange themselves in a definite pattern as shown in fig.

Single touch method: Place the iron bar (or the needle) AB on a table. Take a bar magnet NS and place it almost vertical with its north pole (N) on the end A of the bar.
Move the magnet along tire iron bar till the other end B is reached.

Lift the magnet at the end B and again place it on the first end A Again stroke the bar. Repeat the process about 20 times. Then turn the iron bar AB upside down. Again stroke it with the magnet about 20 times. The bar now becomes a magnet.

Methods of magnetizing a magnetic material are :

1. Single-touch method – A magnet is rubbed along the magnetic substance from one end to another.
2. Double-touch method – Opposite poles of two magnets are placed next to each other at the centre of the magnetic substance and rubbed in opposite direction along it.
3. Magnetizing by induction – It is a method to make temporary magnets under the influence of a magnetizing force. The magnetic properties disappear when the influence of the magnetizing force is removed.
   (A permanent magnet is brought close to the magnetic substance but not touched.)
4. Electric current – A magnet made by using electric current is called an electromagnet. It is a temporary magnet and stops behaving like a magnet when the current is stopped. Electromagnets can become permanent magnets if certain materials like steel and special alloys are placed in a coil and a very strong current is passed through the coil.