Carbon Arc Lamps :
Working principle :
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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)
For which purpose Carbon Arc D.C lamps are mainly used.
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