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Magnetic Effects of Electric Current

Magnetic field and its characteristics

It is clear from the above activity that a current carrying the rod experiences a force when placed between two poles of strong magnets. The direction of displacement of the rod reverses when the direction of current is reversed. This suggests that the direction of force exerted on the rod is related with the direction of current.

Repeat the same process by reversing the direction of the magnetic field. You can easily observe that the rod will displace towards the right when the current flows from Q to P, and displaces towards the left when the current flows from P to Q. What does this suggest?

This suggests that the direction of force exerted on the rod is related with the direction of the magnetic field. Thus, we can say that the directions of current, magnetic field, and magnetic force are perpendicular to each other.

Experimentally, it is found that the magnitude of this force depends upon three factors:

Combining equations (1), (2) and (3) we get $F\propto IBl=KIBl$

where K is a constant and its value in SI unit is 1.
So,    F = IBl

Apply Fleming’s left hand rule to find the direction of this magnetic force.

Fleming’s left hand rule

This rule states that if you stretch the thumb, index finger, and middle finger of your left hand such that they are mutually perpendicular to each other, then your index finger represents the direction of the field, the middle finger represents the direction of the current, and the thumb represents the direction of the force experienced by the conductor.

 A charged particle is moving between two poles of magnets (as shown). Using Fleming’s left hand rule, find out the direction of the magnetic force exerted on the particle?

Do You Know:

 Magnetic field is always produced by an electric current. The ions dissolved in blood move along the nerve cells. Thus, they produce a magnetic field, although a weak one. They produce sensations that we sense through the skin. This is because when we touch, the nerve cells transport an electric impulse to the specific part of our body that we have to use. A short lived magnetic field is produced there, which allows us to sense. Magnetic resonance imaging (MRI) is primarily a technique that uses magnetism, which is produced in our nerve cells to obtain computerised images of internal parts of our body such as the heart, brain etc.

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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 slowl…

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