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THEORETICAL QUESTIONS

THEORETICAL QUESTIONS

  1. 1.       Define the following terms:

(i)         Magnetic flux density

(ii)      Relative permeability

(iii)    Absolute permeability

(iv)    Magnetomotive force.

  1. 2.       State the differences between magnetically soft and magnetically hard materials.
  2. 3.       Sketch the shape of magnetic field around a current-carrying conductor. How can the direction of the field be determined?
  3. 4.       What do you understand by the ferromagnetic, paramagnetic and-diamagnetic materials?
  4. 5.       Sketch the magnetic field that occurs around two adjacent current carrying conductors

(i)         for currents in opposite direction

(ii)      for currents in the same direction.

  1. 6.       Derive an expression for magnetising force of a long straight conductor.
  2. 7.       Derive an expression for magnetising force of a long solenoid.
  3. 8.       Derive an expression for force between two parallel conductors.
  4. 9.       Define the following terms as applied to a magnetic circuit:

Permeability; Magnetomotive force (m.m.f.) ; Reluctance; Permeance ; Reluctivity.

  1. 10.    Give the analogy between electric and magnetic circuits (similarities).
  2. 11.    What do you mean by magnetic leakage and fringing?
  3. 12.    Draw and explain a magnetising curve for a ferromagnetic material.
  4. 13.    Explain briefly the following two types of losses which occur when magnetic materials are subjected to an alternating flux:

(i)      Hysteresis loss

(ii)   (ii) Eddy current loss.

  1. 14.    What do you understand by “electromagnetic induction”.
  2. 15.    Explain briefly Faraday’s first and second laws of electromagnetic induction.
  3. 16.    State and explain Fleming’s right hand rule.
  4. 17.    What is “Lenz’s law”?
  5. 18.    What is difference between the dynamically and statically induced e.m.fs. ?
  6. 19.    Define the term “Self-inductance”.
  7. 20.    Derive an expression for energy stored in an electromagnetic field.
  8. 21.    Explain briefly “Mutually induced e.m.f.”.
  9. 22.    What is “Mutual inductance”?
  10. 23.    What do you understand by “Co-efficient of coupling”?