ELECTROMAGNETISM

1
ELECTROMAGNETISM

• Observation 1 A moving electric charge produces
  a magnetic field in the space around it.
• ( An electric current produces a magnetic field
  around it.)
• Oersteds Effect

2
Electromagnetism Contd

• An application of Oersteds Effect is the
  electromagnet and all the various devices which
  use it.
• Some of these are the telephone receiver, the
  speaker, solenoid and electromagnets which are
  part of all electrical motors. There are giant
  electromagnets which pick up cars and crush them
  by dropping them.

3
Electromagnetism Contd

• Observation 2 A magnetic field exerts a force on
  a moving charge.
• ( The velocity of the charge must be
  perpendicular to the magnetic field)
• F q v B
• (A magnetic field exerts a force on a current
  carrying wire.) F I L B (AMPEREs LAW)
• ( The current must be perpendicular to the
  magnetic
• field.)

4
Electromagnetism Contd

• The application of observation 2 is an
  electric motor. The motor uses a loop of wire
  between the pole faces of an electromagnet or a
  permanent magnet.

5
Electromagnetism Contd

• The force on the two sides (RED) of the loop
  perpendicular to the magnetic field causes the
  loop to rotate, until the sides are parallel to
  the magnetic field.

6
Electromagnetism Contd

• The force on a charge is used to make the
  raster (or lighted area) on all television
  screens and most computer monitors. It is also
  the mechanism for magnification in electron
  microscopes.

7
Electromagnetism Contd

• Observation 3 A moving magnet produces an
  electric field in the space around the coil.
• (A coil of wire of area A having N turns in
  motion relative to a magnet has a current I
  induced in it.)
• Faradays Law
• E I R -N A ? B
• ? t
• where ? B is the change in the magnetic field
  per
• ? t unit of time.

8
Electromagnetism Contd

• An application of Faradays Law is the
  electrical generator. It is the means by which
  electrical energy is generated from mechanical
  energy.
• This effect is the opposite of Amperes Law
• (motor effect) by which electrical energy is
  turned in mechanical energy.