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Basic Electrical interview Questions & Answers paper-2

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21. What is the effect of heat on insulator ?

Ans : Insulator resistance of most solid dielectric with the possible exception of mica and asbestos is decreased with the rise in temperature and increased when cooled.

22. What is the effect of moisture and impurities on insulating materials ?

Ans : Moisture and impurities held in the combined form on the insulating material reduce its resistivity, increase the absorption and dielectric loss and finally reduce the dielectric strength.

23. Why is porcelain glazed for use as outdoor insulators ?

Ans : Outdoor porcelain insulator is glazed to prevent the surface leakage owing to the accumulation of dirt and absorption of moisture. The insulation resistance is also increased by glazing.

24. What are the properties of a good conductor ?

Ans : A good conductor must have the following properties :-
i) Low resistivity,
ii) Less variation in resistance with temperature,
iii)Good mechanical strength,
iV) Less specific weight,
v) High resistance to corrosion and
vi) High ductility.

25. What are the properties of a good insulator ?

Ans : A good insulator must have the following properties :-

  • Non-hygroscopic i.e. it will not absorb moisture,
  • High resistance to corrosion,
  • Good mechanical strength,
  • High insulation resistance and
  • High breakdown voltage.

    26. What are a semiconductor ?

    Ans : A semiconductor is a substance whose resistivity lies in between those of good conductor and insulator. Its resistance decreases with rising temperature and the presence of impurities in contrast to the normal metallic conductor for which normally behaves like an insulator.

    27. What are the different types of semiconductors ?

    Ans : There are two types of semiconductors :
    i) Intrinsic semiconductors in pure form and
    ii)Extrinsic semiconductors with added impurities.
    Extrinsic semiconductors are sub divided into two types depending upon the type of impurity added such as (1)N-type and (2) P-type.

    28. Give some examples of semiconductors ?

    Ans : Germanium (Ge), Silicon (Si), Selenium (Se), Carbon (C) etc.

    29. Where are semiconductors used ?

    Ans : Semiconductors are generally used in electronic devices such as Radio, Television I.C.,V.C.R. etc.

    30. What is resistance ?

    Ans : Resistance is the property of a substance which opposes the flow of electricity through it.

    31. How are resistances classified ?

    Ans : From the point of measurement resistances are classified as follows :-
    i)Low resistances – All resistances of the order of 1 ohm or less.
    ii)Medium resistances – Resistances ranging from about 1 ohm upwards to about 100000 ohms.
    iii)High resistances – Resistances of 100000 ohms and above.

    32. What is the unit of resistance ?

    Ans : The unit of resistance is ‘ohm’.

    33. What is resistor ?

    Ans : Resistor or Rheostat is a device whose chief property is to oppose or resist the flow of electricity.

    34. On what factors does the resistance of a conductor depend ?

    Ans : Resistance of a conductor depends on its (1)Length, (2)Cross section, (3) Resistivity i.e. nature and composition of conductor material, (4) Temperature and (5) Nature of the current flowing through the conductor.

    35. What is the specific resistance of a conductor ?

    Ans : The specific resistance or resistivity of a conductor is the resistance offered by unit metre cube of the material of that conductor.

    36. What is the unit of specific resistance ?

    Ans : Ohm-meter.Type equation here.

    37. What is the relation among resistance, length, and cross sectional area ?

    Ans : Resistance ∝ Length/(Area of cross section) Resistance varies, directly proportional to the length and inversely proportional to the cross section.

    38. What is the effect of heat on resistance ?

    Ans : Resistance is increased with the rise in temperature end decreased when cooled.

    39. What is temperature coefficient of resistance ?

    Ans : Temperature Coefficient of resistance is defined as the change in resistance per degree change of temperature per ohm of resistance.

    40. Define Ohm’s law.

    Ans : Ohm’s law states that at the constant temperature, the current flowing in a circuit is directly proportional to the potential difference across the circuit.

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