Why is a choke coil is needed in the use of fluorescent tubes?Why can we not use ordinary resistor?

Asked by  | 10th Nov, 2008, 08:03: PM

Expert Answer:

A fluorescent lamp works by striking an arc between the two electrodes at the end of the tube. This arc passes through the gas that is filled inside the tube. The emissions from the arc hit the fluorescent coating on the inner surface of the tube to produce light.

A high voltage is required to strike this arc. This is produced by the choke. The choke is nothing but a coil wound over a core; in other words, an inductor. When you switch on the tube light, the sudden surge of current induces a back-EMF across the choke. This voltage is applied across the electrodes of the tube light and it strikes an arc.

Once the arc is struck, the current flows through the gas inside the tube. There is no further point in letting it flow through the choke after the tube glows steadily, as this would only result in losses. Therefore, the choke needs to be cut-off after the tube light glows steadily. This is done by the starter, which cuts off the current through the choke after some time. (It allows the current to flow through the choke only during the starting, and hence it is called a starter).

A resistor due to resistenace leads to losses when current flows through it.Hence it is not used at the place of choke.

Answered by  | 11th Nov, 2008, 05:19: PM

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