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Electrostatic Potential and Capacitance
Question
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Answer the following questions:
Why is choke coil needed in the use of fluorescent tubes with ac mains? Why can we not use an ordinary resistor instead of the choke coil?

Answer

A choke coil is needed in the use of fluorescent tubes to reduce alternating current without loss of power. If we use an ordinary resistor, a.c. will reduce, but loss of power due to heating will be there. 

∴ Power dissipated = Ev Iv cos ϕ
In a resistor, ϕ = 0°
∴ Power dissipated = Ev Iv cos 0°
                            = Ev Iv 
which, is the maximum value. 

In a choke coil, ϕ = 90°
∴ Power dissipated = Ev Iv cos 90° = zero.

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