Changes

===Notes for teachers===

===Notes for teachers===

'''Direction of induced emf :'''  

'''Direction of induced emf :''' <br>

'''Fleming’s right hand rule :''' <br>

'''Fleming’s right hand rule :''' <br>

Stretch the thumb, middle finger and fore finger of your right hand mutually perpendicular to each other as shown in the fig. If the fore finger indicates the direction of magnetic field and the thumb indicates the direction of motion of conductors, then the middle finger will indicate the direction of induced current.  

Stretch the thumb, middle finger and fore finger of your right hand mutually perpendicular to each other as shown in the fig. If the fore finger indicates the direction of magnetic field and the thumb indicates the direction of motion of conductors, then the middle finger will indicate the direction of induced current. <br>

 

'''Lenz’s law :''' It states that the direction of induced emf (or induced current) always tends to oppose the cause which produces it. <br>

'''Lenz’s law :''' It states that the direction of induced emf (or induced current) always tends to oppose the cause which produces it.  

(b) When the north pole of the magnet is brought towards one end of the solenoid, the induced current flows in the solenoid in such a direction that the end of the solenoid, near the magnet and becomes a north pole so as to repel the magnet and thus opposes the cause producing the induced current. Therefore e the direction of induced current in solenoid at its end towards the magnet is anti-clockwise. <br>

(b) When the north pole of the magnet is brought towards one end of the solenoid, the induced current flows in the solenoid in such a direction that the end of the solenoid, near the magnet and becomes a north pole so as to repel the magnet and thus opposes the cause producing the induced current. Therefore e the direction of induced current in solenoid at its end towards the magnet is anti-clockwise.  

(d) When the north pole of the magnet recedes form the end of the solenoid, the direction of induced current in the solenoid is such that the end of the solenoid towards the magnet becomes a south pole so as to attract the north pole of the magnet and thus opposes the cause producing it. The current induced current in solenoid at its end clockwise.

(d) When the north pole of the magnet recedes form the end of the solenoid, the direction of induced current in the solenoid is such that the end of the solenoid towards the magnet becomes a south pole so as to attract the north pole of the magnet and thus opposes the cause producing it. The current induced current in solenoid at its end clockwise.

Lenz’s law is wider significance as it implies the law of conservation of energy. It shows that the mechanical energy spent in doing work, against the opposing force experienced by the moving magnet, is transformed into the electrical energy due to which current flows in the solenoid.  

Lenz’s law is wider significance as it implies the law of conservation of energy. It shows that the mechanical energy spent in doing work, against the opposing force experienced by the moving magnet, is transformed into the electrical energy due to which current flows in the solenoid. <br>

'''A.C. Generator:'''  

'''A.C. Generator:''' <br>

An A.C.generator is a device which converts the mechanical energy into the electrical energy using the principle of electromagnetic induction.  

An A.C.generator is a device which converts the mechanical energy into the electrical energy using the principle of electromagnetic induction. <br>

Frequency of alternating current

''Frequency of alternating current''<br>

In one complete rotation of the coil, we get one cycle of alternating emf in the external circuit. Thus the alternating emf has the frequency equal to the frequency of rotations of the coil.  

In one complete rotation of the coil, we get one cycle of alternating emf in the external circuit. Thus the alternating emf has the frequency equal to the frequency of rotations of the coil. <br>

If the coil makes n rotations per second. The magnitude of induced emf is given as  

If the coil makes n rotations per second. The magnitude of induced emf is given as <br>

E=e0sin2nt

E=e0sin2nt

And the current is expressed as i=i0sin2nt

And the current is expressed as i=i0sin2nt <br>

Where e0 and i0 represent the maximum values of emf and current respectivily. Such a current is called an alternating current.

Where e0 and i0 represent the maximum values of emf and current respectivily. Such a current is called an alternating current.