Page 330 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

Production of heat due to arc:
When carbon electrodes are separated, the electrons move from negative electrode to positive electrode through
air and set the air in ionised condition.
The positive ions move towards the negative electrode and colliding with carbon thereby producing good amount
of heat, similarly negative ions collides with positive carbon electrode and producing enough heat about 4000
degcel.

Due to higher operating temperature the rate of consumption of positive electrode is nearly double than the
negative electrode. Due to this reason the positive electrode is made of twice the cross sectional area of negative
electrode.
When using arc lamp on AC supply both electrodes burn away at equal rates therefore they are made of equal
cross sectional area.

Efficiency is 20 lumen/watt
The negative electrode is generally fixed and positive electrode is placed in adjustable holder and the process is
manual or automatic.

As the lamp needs frequent adjustment to maintain the constant gap between electrodes it is not used in general
purpose. They are only used in cinema projectors, search lights
Gas discharge lamps
A gas discharge lamp is one in which some inert gas is filled in a glass tube having two electrodes sealed in to
each end , which when heating allows the flow of electons through it.
To obtain continues flow of electrons gas is first charged but as the supply is disconnected from the bulb the gas
is discharged.

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CITS : Power - Electrician & Wireman - Lesson 54-59