Question
What is a choke coil? Why is it preferred to resistance in a.c. circuits? In fig. (a), (b) and (c) are shown three a.c. circuits with equal current. If the frequency of e.m.f. be increased, then what will be the effect on the current flowing in them? Explain with reasons.
Solution
A choke coil is an inductor used to block high frequency alternating current in an electrical circuit , while passing lower frequency current or direct current.
A choke coil is preferred over resistances in a.c. circuit because a choke coil has large value of self inductance and hence, the power dissipation is 0 for choke coil.
Power factor is 0 for an inductance.
In fig. 1 there will be no effect on the flow of current as resistance is independent of frequency.
In fig. 2 since , when frequency is doubled impedence increases and thus, flow of current decreases.
In fig. 3 the flow of current will increase as the capacitive reactance decreases when the frequency is doubled.
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