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rasmy
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What is an electromagnet
An electromagnet is a temporary strong magnet made from a piece of soft iron when current flows in the coil wound around it
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What is lens law?
It states that the direction of induced emf is such that it always tends to oppose the cause which produced it
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What is electromagnetic induction ?
Whenever there is a change in the number of magnetic field lines associated with a conductor an emf is developed between the ends of the conductor which lasts as long as the change is taking place.
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 State the right hand thumb rule?
IF we hold the current carrying conductor in the right hand such that the thumb points in the direction of flow of current then the fingers encircle the wire in the direction of the magnetic field lines
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A coil is moved in a varying magnetic field. name the law which determines the direction of current induced in the coil
Flemings right hand rule
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 What is a solenoid?
A conducting wire is wound in the form of a cylindrical coil whose diameter is less in comparison to the length the coil is called a solenoid
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State Faradays law of electromagnetic induction
- Whenever there is a change in the magnetic flux linked with the coil, an emf is induced. it lasts as long as there is a change in the magnetic flux linked with the coil
- The magnitude of the emf induced is directly proportional to the rate of change of magnetic flux linked with the coil.
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What kind of energy change takes place when a magnet is moved toward a coil having a galvanometer at its end
Mechanical energy --- > electrical energy
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What factor determines the direction of the induced emf
the direction of the induced emf is determined by the change of direction of motion or polarity of the magnet
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 What is the clock rule?
Clock wise current --- South pole
Anticlockwise current --- North pole
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State two factors on which the magnitude of the induced emf depend?
1. Change in the magnetic flux
2. the time in which the magnetic flux changes
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The current is induced in a closed circuit only if there is _____________
Change in number of magnetic field lines linked with the circuit
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What factor determines the direction of induced emf
The direction of the induced emf is determined by the change of direction of motion or polarity of the magnet
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State Flemings left hand rule
 Stretch the forefinger, middle finger and the thumb of your left hand mutually perpendicular to each other . If the fore finger indicated the direction of the magnetic field and the middle finger indicates the direction of the current , then the thumb will indicate the direction of motion of the conductor
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State Flemings right hand rule
 Stretch your thumb, middle finger and fore finger of your right hand so that they are mutually perpendicular to each other.- If the forefinger indicates the direction of the magnetic field and the thumb the direction of the motion of conductor then the middle finger will indicate the direction of the induced current
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How is the magnetic field due to a straight current carrying wire affected if the current in wire is a) decreased b) reversed
a) on decreasing the current the magnetic field lines become less dense and the iron filings get reduced in the size and come closer to the wire
b) When the direction of current in the wire is reversed the pattern of iron filings do not change but the direction of deflection changes
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State a law which determines the direction of magnetic field around a current carrying wire
Right hand thumb rule
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A wire bent into a circle, carries current in an anticlockwise direction . What polarity does this face of coil exhibit?
North
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What is the direction of magnetic field at the centre of a coil carrying current in a) clockwise b) anticlockwise direction
a) Along the axis of the coil inwards
b) Along the axis of the coil outwards
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State two ways by which the magnetic field due to a solenoid can be made stronger
1. the magnetic field can be increased , if the number of turns in the solenoid of given length is increased
2. the magnetic field can also be increased if a soft iron core is placed along the axis of the solenoid
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State two factors on which the strength of magnetic field of an electromagnet depends
1. increase the number of tuens of winding in the solenoid
2. increase the current through the solenoid
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Name three uses of electromagnet
1. in electrical devices like the electric bell, relay microphone
2. For loading furnaces with iron
3. for lifting and transporting huge masses of iron scrap
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State two advantages of a electromagnet over a permanent magnet
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Draw the diagram of the electric bell and learn its working
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Is the working of an electric bell affected if ac current is use instead of direct current?
If an ac source is used the core of the electromagnet will get magnetized, but the polarity at its ends will change. Since attraction of armature does not depend on the polarity the bell will still ring when switch k is pressed
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