Magnetic Field Reversal

Magnetic effects of current

Electromagnetic induction

Whenever there is a relative motion between a magnet and a coil, a current is induced in the coil due to the change in the magnetic field associated with it. This process of producing induction current is known as electromagnetic induction.

Take a small aluminium rod AB .Using two connecting wires suspend it horizontally . Place a strong horse-shoe magnet in such a way that the rod lies between the two poles with the magnetic field directed upwards. For this put the north pole of the magnet vertically below and south pole vertically above the aluminium rod (Fig. 13.12).Now pass a current through the aluminium rod from end B to end A.Reverse the direction of current flowing through the rod.

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Write down your observation with reason.

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What wil happen if we reverse the poles of the battery or magnet?

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On what factors does the force experienced by the rod depend?

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What will happen if the direction of current flowing in the rod is parallel to the direction of magnetic field?

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Write down the condition for which the rod will experience the maximum displacement?

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What will happen if we decrease the length of the rod?

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What will happen if we connect the rod with a ac source in place of a dc source?

Take two different coils of copper wire having large number of turns (say 50 and 100 turns respectively). Insert them over a non conducting cylindrical roll,

Connect the coil-1, having larger number of turns, in series with a battery and a plug key.

Also connect the other coil-2 with a

galvanometer as shown. Plug in the key.

Disconnect coil-1 from the battery.

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What are the names of two coils?

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Why there are more no. of turns on first coil?

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Can we wrap insulated copper wire on a cardboard sheet.Give reason for your answer.

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Write down your observations when the key is plugged in.

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Why there is momentary deflection when the key is plugged in in the first coil?

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What will happen if we replace dc source with an ac source in the first coil?

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Which rule is used to find the direction of induced current?

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How can we increase induced current in this activity?

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Electromagnetic induction is main principle for which electric device?

Activity

Take a coil of wire AB having a large number of turns.n Connect the ends of the coil to a galvanometer as shown .

Take a strong bar magnet and move its north pole towards the end B of the coil.

Now withdraw the north pole of the magnet away from the coil.

Place the magnet stationary at a point near to the coil, keeping its north pole towards the end B of the coil.

now the coil is moved towards the north pole of the magnet. Similarly now the coil is moved away from the magnet.

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Take a strong bar magnet and move its north pole towards the end B of the coil. Do you find any change in the galvanometer needle?

give reason for the answer.

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Now withdraw the north pole of the magnet away from the coil. Write your observation.

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Now keep the magnet stationary and move the coil towards the magnet,what will happen.Also if the process is reversed.

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Now the coil is kept stationary with respect to the magnet, Write your observations.

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The coil we used should have large no. of turns why?

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Why there is momentary deflection in the galvanometer?

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On what factors does induced potential difference depend?

ACTIVITY 13.1

Take a straight thick copper wire and place it between the points X and Y in an electric circuit, as shown in Fig. 13.1. The wire XY is kept perpendicular to the plane of paper.

Horizontally place a small compass near to this copper wire.Pass the current through the circuit by inserting the key into the plug.

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Write down any two observations.Give reason for your answer.

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Write two ways for obtaining pattern of magnetic field lines around the wire.

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What will happen if the poles of battery will reversed?

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Does the no. of times you wrap the wire around the nail affect the strength of the magnet ? Give reason.

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Does the thickness or length of the nail affect the electromagnet strength? Give reason.

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Does the thickness of wire affect the power of the electromagnet? Give reason for your answer.

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What is a solenoid? What type of magnetic field is produced by a current carrying solenoid?

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What type of magnetic field lines are produced outside the solenoid and inside the solenoid.