Carbon Arc Lamps (D.C. carbon arc lamp)

Carbon Arc Lamps :
Working principle :

  • Two carbon rods kept face to face touching to each other connected to the source of electricity and if they are departed from each other to form a small air gap between them, an arc is produced with tremendous heat and a light is produced.

(a) D.C. carbon arc lamp

Construction :
Figure (d)
  • Two electrodes (1) and (2) placed touching to each other face to face as shown in Figure (d)
  • D.C. supply is about 40 to 60 volts.
  • When current flows, rods Soon become incandescence due to high resistance of carbon.
  • Now if they are slightly pulled so that a gap of about 2 to 3 mm is formed, an arc is formed between them in the gap and a white light is produced.
Figure (e)
  • Transfer of carbon particles from one rod to the other rods maintain the arc in the gap.
  • Due to transfer of particles of carbon the positive rod after some period becomes hollow and negative rod becomes as a pointed pencil as shown in Figure (e)
  • Both rods burn out after some period. Rate of burning of positive rod is twice the negative rod So cross-section of positive rod is made twice of the cross section of negative rod.
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Carbon Arc Lamps (A.C. carbon arc lamp) 


  1. For which purpose Carbon Arc D.C lamps are mainly used.
    Please reply.

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