The above activity indicates that there is a relationship between the direction of the current, the field and the motion of the conductor.

5.3 Force on a current carrying conductor in a magnetic field

        Electric current flowing through a conductor produces a magnetic field. The field so produced exerts a force on a magnet placed in the vicinity of the conductor. French scientist Andre Marie Ampere (1775-1836) suggested that the magnet must also exert an equal and opposite force on the current carrying conductor.

        In the above activity it is seen that the aluminum rod is displaced which suggests that force is exerted on the rod carrying the current when placed in a magnetic field.

Fleming’s left hand rule

Stretch the forefinger, the central finger and the thumb of your left hand mutually perpendicular to each other. If the forefinger shows the direction of the field and central finger shows the direction of the current, then the thumb will point towards the direction of the motion of the conductor. (Fig.5.12)

Fig. 5.12
Fig. 5.12 Fleming's Left Hand Rule

        The direction of the force depends on the direction of the current and the direction of magnetic field. The displacement of the rod is maximum when the direction of current is at right angles to the direction of magnetic field. Fleming’s left hand rule Stretch the forefinger, the central finger and the thumb of your left hand mutually perpendicular to each other. If the forefinger shows the direction of the field and central finger shows the direction of the current, then the thumb will point towards the direction of the motion of the conductor. (Fig.5.12)

        Current is a flow of charge. This means that moving charges in a magnetic field would experience a force. This property is used to accelerate charged particles to very high energies. These high energies of the particles are used to study the structure of matter.

Use of magnetism in medical sciences

        Electric current produces magnetic field, even if the current is very weak.
        Ion current (very weak) which travels along the nerve cells in our body produces magnetic fields. If we touch something, our nerves carry an electrical impulse to the muscles we need to use. This produces weak magnetic field. Heart and brain are the two main organs where significant magnetic fields can be produced. This forms the basis of obtaining images of heart and brain or images of different parts of the body. This is done using a technique called Magnetic Resonance Imaging (MRI). Analysis of these images help doctors to diagnose disorders of the brain.


Activity 5.8
Fig. 5.13

Take three ring shaped magnets, insulated copper wire (1.5m), battery and paper clips. Cut the wire into three pieces. One piece should be about 1m long and the other two, 0.25m long each. Take 1m piece of wire and wrap this around two fingers to form a coil. Take the loose end of this wire and wrap it once along the diameter of the coil. The two arms of the coil should be directly opposite to each other. Bend the paper clip and prepare a holder for the coil. Pile the three magnets on the table. Place the coil above the magnet on the paper clip holder. Take free ends of the wire and connect them to the battery as shown in figure 5.13. Give a gentle spin to the coil. What do you observe? Answer


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