Magnet for standard 8 to 12 physics practical

Mechanical method of Magnet making 

Magnet making process

Mechanical method

Take an iron nail or a needle. Keep it horizontally on a table. Take a bar magnet. Rub the nail from any one end to the other (in only one direction), with any one pole of the bar magnet. Repeat this many times without changing the pole or the direction of rubbing. The nail becomes magnetised (fig ). This process of magnetising by rubbing with a magnet is called mechanical method.

Do it yourself

Take a clean test-tube and fill it with iron filings. Close its mouth with a rubber cork. Observe the arrangement of iron fillings. Keep any one pole of a bar magnet near one end of the test tube. Rub that test tube with this pole along its surface in one direction (fig 1.14(a)), Repeat the rubbing without changing the pole and direction of rubbing. Now observe the arrangement of iron fillings in the test tube. Bring one end of the test tube near the north pole of a magnetic needle. What do you observe ? (fig 1.14(b)(. Bring the same end of the test tube near the south pole of the magnetic needle. What do you observe ? Record your observations. Shake the test tube and again bring the ends of the test tube near the poles of the magnetic needle and observer. Explain your observations with reasons.

Electric Magnet

Making a Magnet by Electric method 

Electromagnet making process

Electronagnet

Electrical method

Wind a good length of insulated copper wire around a steel bar which is to be magnetised. Connect the ends of the wire to the poles of a battery. When the electric current passes through the copper wire the steel bar becomes a magnet. (fig). If a soft iron bar is used. It becomes a strong magnet temporarily. It loses its magnetism as soon as the current in the copper wire is switched off. Such temporary magnets are called electromagnets.

Electric Magnet:-
An electromagnet is a device in which magnetism is produced by an electric current.
British electrician, William Sturgeon invented the electromagnet in 1825. The first electromagnet was a horseshoe-shaped piece of iron that was wrapped with a loosely wound coil of several turns. When a current was passed through the coil; the electromagnet became magnetized and when the current was stopped the coil was de-magnetized. Sturgeon displayed its power by lifting nine pounds with a seven-ounce piece of iron wrapped with wires through which the current of a single cell battery was sent.
Sturgeon could regulate his electromagnet; this was the beginning of using electrical energy for making useful and controllable machines and laid the foundations for large-scale electronic communications. Five year later an inventor called Joseph Henry - made a far more powerful version of the electromagnet. American, Joseph Henry(1797-1878), demonstrated the potential of Sturgeon's device for long distance communication by sending an electronic current over one mile of wire to activate an electromagnet which caused a bell to strike. Thus the electric telegraph was born.

Magnetic lines of force Practical for standard 8 to 12

 Experiment 1:   
Magnetic lines of  force around a bar magnet. 

Aim :- 
To draw the magnetic lines of force around a bar magnet.

Materials required :- 
Drawing board, brass pins, a sheet of paper, a bar magnet, a magnetic compass, a pencil and a scale. 

Procedure :-  Fix the paper on the drawing board using brass pins so that there are no wrinkles. Place the compass in the middle of the sheet and mark the North-South direction by putting dots against the poles. Remove the compass and draw a straight line through these dots.

Note :- 
Do not disturb the drawing board till the experiment is complete. 

 

Northe South direction

Magnetic lines of force around magnet

Special instruction

The compass may not show any  specific direction at certain places around the magnet and may behave indifferently. Locate such points. (neutral points).

On the basis of your observations in the above experiment state whether the following  statements are
true or false. Correct if necessary.

1.The magnetic lines of force start at one pole and end at the other.

2.The magnetic lines of force do not intersect each other.

3.The pattern of the magnetic lines of force depends on the position of the magnet with respect to the geographical poles of the earth.

Remember

 The magnetic lines of force start at one pole and end in the   other. But conventionally the lines of force are considered   to start at the north pole and end in the south pole.

 The magnetic lines of force do not intersect each other.

Magnetic field : 

Experiments have shownthat a magnet or a current carrying conductor can exert force on the nearby magnetic substances even when they are not in touch with each other. It implies that there is a magnetic force around a magnet or a current carrying conductor. The area in which magnetic force is present and magnetic effect is felt is called magnetic field. 

Detection of the presence of a magnetic field.
Keep a magnetic needle in the area to be tested. If the magnetic needle deflects, then it means that there is a magnetic field. Usually magnetic field is represented by a set of lines. These lines are called magnetic lines of force. Why is magnetic field represented by a set of lines ? Magnetic field or magnetic lines of force are invisible. The fact that the iron filings arrange themselves along a few curved lines (fig 1.12(b)) in a magnetic field might have resulted in the concept of lines of force. The magnetic lines of force can also be traced by a magnetic needle. The pattern of magnetic lines of force depends on the shape of the magnet and its strength. Therefore the pattern of magnetic lines will be different for different magnets. The study of magnetic lines of force around a powerful bar magnet reveals the following properties.