A solenoid with inductance L = 7mH and active resistance R = 44 Ω is first connected to a source of direct voltage V 0 and then to a source of sinusoidal voltage with effective value V = V 0 . At what frequency of the oscillator will the power consumed by the solenoid by η = 5.0 times less than in the former case?
Text Solution
Verified by ExpertsThe correct answer is:
CHECK THE SOLUTION.
Sol. In the case of direct current,
P DC = 
AC Circuits
The impedance of LR circuit is
= 
∴ I M = 
= 
∴ P AC = 
= 
According to problem,
P DC = η P AC
or 
= η 
or 
= 
or 
= 
or 
= η
or 
= 
or ω = 
or 2 πν = 
v = 
= 2 kHz
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