You know that an 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 a conductor.
French scientist Andre Marie Ampere suggested that the magnet must also exert an equal and opposite force on the current carrying conductor.
ACTIVITY
Aim : To study the forece experienced by a current carrying conductor in a magneticfield.
What do you need ?
A U-shaped magnet, two batteries, two rheostats, one tapping key, one plug key, two ammeters, mercury in a shallow dish, a flexible joint J and connecting wires.
What to do ?
(i) Place the dish containing mercury between the pole pieces of the electromagnet.
(ii) From a rigid support T, suspend flexible joint J.
Let the thick copper wire AB hang on J so that its lower end B just touches mercury.
(iii) Connect the positive terminal of the battery with J and the negative terminal to a rheostat which is
connected to an ammeter and a tapping key. Wire from the other end of the tapping key is dipped in
mercury.
(iv) Connect a battery, a rheostat, an ammeter and a plug key across the electromagnet as shown in fig.
(v) Insert plug in key K2 and press K1.
(vi) Repeat the experiment by increasing current in the electromagnet and the wire AB, one by one.
What do you observe ?
You will observe that (i) on pressing key, the wire AB swings out of the pole pieces of the electromagnet, (ii) the amplitude of swing increases when the strength of the electromagnet is increased by increasing the current in it or when the current in the wire is increased.
What do you infer ?
(i) A current carrying conductor placed in a magnetic field experiences a force due to which the conductor moves out of the mercury cup, as a result of which the circuit breaks and wire falls back and swings in and out of the mercury cup.
(ii) The force increases with an increase in the current flowing through the conductor.
(iii) The magnitude of the force also increases with the increase in the strength of the magnetic field.
The direction of the force experienced by a conductor placed in a magnetic field is perpendicular
to the direction of current as well as magnetic field and is given by Fleming’s Left Hand Rule. According to this rule,
if you hold the forefinger, the central finger and the thumb of your left hand at right angles to
each other in such a way that the forefinger points in the direction of magnetic field and the central finger is in the direction of current, then, the thumb will indicate the direction of the force experienced by the conductor
For example,
if we consider a horizontal magnetic field running west to east in which a conductor hangs vertically and the current in it flows in a vertically downward direction, then the wire will experience
a force in southward direction
French scientist Andre Marie Ampere suggested that the magnet must also exert an equal and opposite force on the current carrying conductor.
ACTIVITY
Aim : To study the forece experienced by a current carrying conductor in a magneticfield.
What do you need ?
A U-shaped magnet, two batteries, two rheostats, one tapping key, one plug key, two ammeters, mercury in a shallow dish, a flexible joint J and connecting wires.
What to do ?
(i) Place the dish containing mercury between the pole pieces of the electromagnet.
(ii) From a rigid support T, suspend flexible joint J.
Let the thick copper wire AB hang on J so that its lower end B just touches mercury.
(iii) Connect the positive terminal of the battery with J and the negative terminal to a rheostat which is
connected to an ammeter and a tapping key. Wire from the other end of the tapping key is dipped in
mercury.
(iv) Connect a battery, a rheostat, an ammeter and a plug key across the electromagnet as shown in fig.
(v) Insert plug in key K2 and press K1.
(vi) Repeat the experiment by increasing current in the electromagnet and the wire AB, one by one.
What do you observe ?
You will observe that (i) on pressing key, the wire AB swings out of the pole pieces of the electromagnet, (ii) the amplitude of swing increases when the strength of the electromagnet is increased by increasing the current in it or when the current in the wire is increased.
What do you infer ?
(i) A current carrying conductor placed in a magnetic field experiences a force due to which the conductor moves out of the mercury cup, as a result of which the circuit breaks and wire falls back and swings in and out of the mercury cup.
(ii) The force increases with an increase in the current flowing through the conductor.
(iii) The magnitude of the force also increases with the increase in the strength of the magnetic field.
The direction of the force experienced by a conductor placed in a magnetic field is perpendicular
to the direction of current as well as magnetic field and is given by Fleming’s Left Hand Rule. According to this rule,
if you hold the forefinger, the central finger and the thumb of your left hand at right angles toeach other in such a way that the forefinger points in the direction of magnetic field and the central finger is in the direction of current, then, the thumb will indicate the direction of the force experienced by the conductor
For example,
if we consider a horizontal magnetic field running west to east in which a conductor hangs vertically and the current in it flows in a vertically downward direction, then the wire will experience
a force in southward direction
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