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Electrical Power Generation interview question and answers


  1. Answer :
    It is defined as the total quantity of light energy emitted per second from a luminous body. 
    • It is represented by symbol F and is measured in lumens. 
    • The conception of luminous flux helps us to specify the output and efficiency of a given light source.
  2. Answer :
    It is defined as the luminous per unit projected area of either a surface source of light or a reflecting surface and is denoted by L.
  3. Answer :
    Law of Inverse squares:
    Illumination at a point is inversely proportional to square of its distance from the point source and directly proportional to the luminous intensity (CP) of the source of light in that direction.
    • If a source of light which emits light equally in all directions be placed at the centre of a hollow sphere, the light will fall uniformly on the inner surface of the sphere. 
    • If the sphere be replaced by one of the larger radius, the same total amount of light is spread over a larger area proportional to the square of the radius.
    Lambert’s cosine law:
    The illumination at a point on a surface is proportional to cosine of the angle which ray makes with the normal to the normal to the surface at that point.
  4. Answer :
    It is defined as the number of lumens given out by the source in a unit solid angle in a given direction. 
    It is denoted by CP
    Cp = lumens /ω
  5. Answer :
    The mean of candle power in all directions in the horizontal plane containing the source of light is termed as Mean Horizontal Candle Power.
  6. Answer :
    As per the principle of operation the light sources may be grouped as follows:
    1. Arc lamps
    2. High temperature Lamps
    3. Gaseous Discharge Lamps
    4. Fluorescent type Lamps
  7. Answer :
    It is defined as the ratio of total lumens reaching the working plane to total lumens given out by the lamp
    utilisation factor  = [Total lumens reaching the working plane] / [Total lumens given out by the lamp]
  8. Answer :
    1. Bunsen head or Grease spot photometer
    2. Lummer-brodhun photometer head
    There are two types of lummer brodhun heads:
    1. Equality oc Brightness type photometer head
    2. Contrast type photometer head
  9. Answer :
    • In most lamps or sources of light the luminous intensity is not the same in all directions. 
    • If the luminous intensity, ie, the candle power is measured in a horizontal plane about a vertical axis and a curve is plotter between candle power and the angular position, a curve obtained is called as horizontal polar curve.
    • The luminous intensity in all the directions can be represented by polar curves. 
    • If the luminous intensity in a vertical plane is plotted against position, a curve known as vertical polar curve.
  10. Answer :
    It is defined as the ratio of horizontal distance between adjacent lamps and height of their mountings.
    Space-height ratio = [Horizontal distance between two adjacent lamps] / [Mounting height of lamps above working plane]

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