Magnetic Effects of Electric Current

QUESTIONS :

  1. What do you understand by live, neutral and earth wires? Do all the three normally carry electricity?

  2. What is the function of the earth wire in electric lines? Why is the metallic body of an electric appliance connected to the earth wire?

  3. What is short circuit? How does a fuse help in case there is short circuit?
  4. What is the frequency of AC supply in India?
  5. Name some sources of direct current.
  6. Which sources produce alternating current?

REVIEW :

  1. Magnetic field : It is the space around a magnet in which the force of attraction or Repulsion due to the magnet can be detected. It has both magnitude and direction.

  2. Magnetic field lines : It is the curved paths along which the iron filings arrange
    Themselves due to the force acting on them in the magnetic field of the bar magnet.

  3. Properties of Magnetic field lines:
    1. It starts from the north pole of a magnet and end at its south pole.
    2. It is a closed and continuous curve.
    3. They do not intersect one another.
    4. They come closer to one another near the poles of a magnet but they are widely separated at other places.
  4. Oersted experiment : This experiment demonstrated that around every conductor carrying an electric current, there is a magnetic field. The direction of deflection of the needle due to magnetic field of a current carrying conductor is given by Ampere’s Swimming Rule.

  5. Magnitude of Magnetic field due to a current carrying straight conductor :
    ( µo I ) / (2 π r)
    Where B = Magnetic field
    µo = Permeability of vacuum
    I = Current flowing in conductor.
    R = Distance from the conductor.
    The magnetic lines of force round a straight conductor carrying current are concentric circles whose centers lie on the wire.
    The direction of magnetic field produced by is given by a straight conductor carrying current Right –Hand Thumb Rule.
    The SI unit of magnetic field is Tesla (T).

  6. Magnetic field due to a current carrying circular coil
    A circular coil consists of twenty or more turns of insulated copper wire closely wound together. The magnetic field produced at the center of a circular wire of radius r and carrying a current I is given by:
    o I )/ (2r )mMagnetic field, B = (
    o = Permeability of free space (constant)mWhere
    I = Current flowing through the wire
    r = radius of the circular wire

  7. Solenoid : It is a coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder.
    The magnetic field produced by a current carrying solenoid is similar to the magnetic field produced by a bar magnet. The strength of magnetic field produced by a current carrying solenoid depends on: The number of turns in the solenoid
    β The strength of current in the solenoid
    β The nature of core material used in making solenoid

  8. Electromagnets and Permanent Magnets
    1. Electromagnets : It works on the magnetic effect of the current. It consists of a long coil of insulated copper wire wound on a soft iron core. The core of the electromagnet must be of soft iron because soft iron looses all of its magnetism when coil is switched off.

    2. Permanent Magnets: a permanent magnet is made from steel. As steel has more retentivity than iron, it does not lose its magnetism easily.
      Apart from steel alloys like Alnico (Aluminium, Nickel-Cobalt, alloy of iron) and Nipermag (an alloy of Iron, Nickel, Aluminium and Titanium) are used to make very strong permanent magnets.

  9. Force on current carrying conductor placed in magnetic field
    When a current carrying conductor is placed in a magnetic, a mechanical force is exerted on the conductor which can make the conductor move.
    The direction of the force is given Flemings left hand rule.
    The magnitude of force acting on a current carrying conductor placed in a magnetic field
    F = B × I ×L
    Where
    B= magnitude of magnetic field
    I = current flowing in the wire
    L= length of the current-carrying wire placed in the magnetic field

  10. Electric motor : A motor is a device which converts electrical energy into mechanical energy.
    A motor works on the principle that whenever a current carrying conductor is placed in a magnetic field, it experiences a force given by Fleming’s left hand rule.

  11. Electromagnetic induction: It is the phenomenon of producing induced current in a moving conductor or coil in a magnetic field. It was discovered by Faraday. The direction of the induced current is given by Fleming’s right hand rule.
    The potential difference corresponding to induced current is induced potential difference (pd) or induced electromotive force (emf).

  12. Electric generator: It converts mechanical energy into electrical energy. It works on principle of electromagnetic induction.

  13. Direct current and alternating current : The current which does not change in direction and magnitude is called direct current (D.C).
    The frequency of the D.C current is zero.
    The current which changes its magnitude and direction after a certain fixed interval of time is called alternating current.
    The frequency of the alternating current in India is 50 HZ.

  14. Domestic electric circuits : Usually there are two separate circuits in a house, the lighting circuit with a 5A fuse and the power circuit with a 15A fuse.
    All electrical appliances like bulbs, fans and sockets, etc., are connected tin parallel across the live wire and neutral wire.
    To avoid the risk of electric shocks the metal body of an electrical appliance is “earthed”.

 

CBSE Magnetic Effects of Electric Current Class X ( By Mr. Basant )
Email Id : basant.physics@gmail.com

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