Deck 21: Alternating Current

Question 1

The voltage supplied to an ac circuit is given by $\mathrm{v}(\mathrm{t})=(120 \mathrm{~V}) \sin (377 \mathrm{t})$ . What is the voltage at $\mathrm{t}=3.00 \times$ $10^{-3} \mathrm{~s}$ ?

A) $109 \mathrm{~V}$
B) $63.0 \mathrm{~V}$
C) $119 \mathrm{~V}$
D) $2.37 \mathrm{~V}$
E) $0.00 \mathrm{~V}$

Answer 1

$109 \mathrm{~V}$

Question 2

A $150 \mathrm{~W}$ light bulb is operating on a $120 \mathrm{~V}$ rms ac line. What is the rms current in the bulb?

A) $1.67 \mathrm{~A}$
B) $1.50 \mathrm{~A}$
C) $2.50 \mathrm{~A}$
D) $0.883 \mathrm{~A}$
E) $1.25 \mathrm{~A}$

Answer 2

$1.25 \mathrm{~A}$

Question 3

What is the capacitive reactance of an $8.00 \mu \mathrm{F}$ capacitor attached to $120 \mathrm{~V}$ rms at $60.0 \mathrm{~Hz}$ ?

A) $663 \Omega$
B) $166 \Omega$
C) $332 \Omega$
D) $480 \Omega$
E) $960 \Omega$

Answer 3

$332 \Omega$

Question 4

What is the rms current for an $8.0 \mu \mathrm{F}$ capacitor attached to a $120 \mathrm{~V}$ rms $60 \mathrm{~Hz}$ source?

A) $1.4 \mathrm{~A}$
B) $2.8 \mathrm{~A}$
C) $0.72 \mathrm{~A}$
D) $0.36 \mathrm{~A}$
E) $0.18 \mathrm{~A}$

Question 5

What is the capacitance of a capacitor with a reactance of $20.0 \Omega$ at a frequency of $60.0 \mathrm{~Hz}$ ?

A) $50.0 \mathrm{mF}$
B) $133 \mu \mathrm{F}$
C) $833 \mu \mathrm{F}$
D) $133 \mathrm{mF}$
E) $50.0 \mu \mathrm{F}$

Question 6

What is the inductive reactance of a $200 \mathrm{mH}$ inductor attached to a $120 \mathrm{~V}$ rms, $60.0 \mathrm{~Hz}$ source?

A) $940 \Omega$
B) $24.0 \Omega$
C) $12.0 \Omega$
D) $75.4 \Omega$
E) $188 \Omega$

Question 7

If the power factor for a series RLC circuit is 1.0, what is the phase constant?

A) $90^{\circ}$
B) $0.0^{\circ}$
C) $30^{\circ}$
D) $60^{\circ}$
E) $45^{\circ}$

Question 8

A series RLC circuit has $\mathrm{R}=200 \Omega, \mathrm{L}=40.0 \mathrm{mH}$ , and $\mathrm{C}=120 \mathrm{pF}$ . What is the impedance of this circuit at resonance?

A) $36.0 \mathrm{k} \Omega$
B) $300 \Omega$
C) $200 \Omega$
D) $18.0 \mathrm{k} \Omega$
E) $400 \Omega$

Question 9

A series RLC circuit has resistance $200 \Omega$ , inductance $0.200 \mathrm{H}$ , and capacitance $0.500 \mu \mathrm{F}$ . If the circuit is at resonance with a $120 \mathrm{~V}$ rms source, what is the average power dissipated?

A) $77.0 \mathrm{~W}$
B) $100 \mathrm{~W}$
C) $144 \mathrm{~W}$
D) $120 \mathrm{~W}$
E) $72.0 \mathrm{~W}$

Question 10

What inductance is needed in series with a $4.7 \mu \mathrm{F}$ capacitor for a resonant frequency of $10 \mathrm{kHz}$ ?

A) $0.66 \mu \mathrm{H}$
B) $5.3 \mathrm{mH}$
C) $54 \mu \mathrm{H}$
D) $22 \mu \mathrm{H}$