Rl Circuits - Study Mode

[#11] When the frequency of the voltage applied to a series RL circuit is decreased, the impedance
Correct Answer

(A) Decreases

[#12] A 12 kΩ resistor is in series with a 90 mH coil across an 8 kHz ac source. Current flow in the circuit, expressed in polar form, is I = 0.3 ∠0° mA. The source voltage, expressed in polar form, is
Correct Answer

(A) 3.84 ∠20.6° V

[#13] A 47 Ω resistor is in series with an inductive reactance of 120 Ω across an ac source. The impedance, expressed in polar form, is
Correct Answer

(D) 129 ∠68.6° Ω

[#14] If a load is purely inductive and the reactive power is 12 VAR, the apparent power is
Correct Answer

(B) 12 VA

[#15] In a series RL circuit, 12 V rms is measured across the resistor and 14 V rms is measured across the inductor. The peak value of the source voltage is
Correct Answer

(B) 26.0 V

Explanation

Solution: $$eqalign{
& {{ ext{E}}_{{ ext{rms}}}} = sqrt {{ ext{V}}_{ ext{L}}^2} + { ext{V}}_{ ext{R}}^2 cr
& Rightarrow {{ ext{E}}_{{ ext{rms}}}} = sqrt {{{12}^2}} + {14^2} = sqrt {340{ ext{V}}} cr
& {{ ext{E}}_{{ ext{max}}}} = {{ ext{E}}_{{ ext{rms}}}}sqrt 2 cr
& {{ ext{E}}_{{ ext{max}}}} = sqrt {680{ ext{V}}} cr
& Rightarrow {{ ext{E}}_{{ ext{max}}}} = 26.0,{ ext{V}} cr} $$