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Magnetic Effects of Electric Current

Magnetic field and its characteristics

Construct a simple circuit with open ends M and N. Take a thick conducting wire of aluminium and connect it between the open ends. Now, place a magnetic compass near the aluminium wire and note the position of the compass needle. Now, close the switch to allow the current to flow through the wire and notice the deflection in the needle.

It can be concluded from this activity that electric current flowing through aluminium wire has produced a magnetic force that is exerted on the compass needle resulting in its deflection. Can we say that a magnetic field is related to an electric current?

 Hans Christian Oersted (1777-1851) was the first scientist to observe that a compass needle gets deflected when placed near a current carrying conductor. By this, he concluded that electricity and magnetism are related to each other and called it electromagnetism.

Magnetic lines of force (magnetic force)

You know that a bar magnet can repel or attract another magnet depending on the nature of poles of the other two magnets that are facing each other. When a bar magnet is suspended by thread, its one end always points towards the geographic North Pole, called magnetic North Pole and the other end always points towards the geographic South Pole, called magnetic South Pole of the magnet.

Like poles repel and unlike poles attract each other.

Take a drawing cardboard and sprinkle some iron filings on it. Notice the position of the iron filings as a whole. Now, take a bar magnet and slowly bring it below the cardboard. You will observe that the iron filings tend to attract towards the magnet.

It is observed that most of the iron filings align themselves at poles. What does the pattern represent? It represents that the magnet exerts a force around its body with a stronger force near the two poles. A magnet produces a magnetic field, which can be detected by the force exerted on the iron filings. The regular pattern of the iron filings on the board represents the lines of magnetic field or lines of magnetic force called magnetic lines.

How to determine the shapes of magnetic field lines of a bar magnet?

To understand the process, let us see this animation

Do you know the direction of a magnetic field inside the magnet?

Inside the magnet, magnetic field lines run from the South Pole to the North Pole where they emerge out. Therefore, we can say that magnetic field lines make closed curves.

• The region where magnetic field lines are crowded has relatively greater strength. Hence, in a magnet, strength of the regions near the poles is greater than other regions.
• It should be noted that a compass needle cannot point in two directions when placed at a point near the magnet. This means that no two magnetic field lines cross each other at a point.

Characteristics of magnetic field lines

1. Magnetic field lines emanate from the North Pole and terminate at the South Pole of a magnet. (Outside the magnet)
2. The degree of closeness of magnetic field lines represents the relative strength of the magnet.
3. No two field lines can intersect each other.

Magnetic field lines of the Earth

The Earth is treated as magnetic because it is assumed that a huge bar magnet is buried within its interior with the magnetic North Pole near the geographic South Pole, and the magnetic South Pol...

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