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Lesson 26
(1) The AC current through a 50Ω resistor has a
maximum of 3.0A. What is the average power
dissipated in the resistor?
(2) Calculate the reactance of a 30μF capacitor at a
frequency of 50kHz.
What is the reactance when the frequency is
50Hz?
What is the reactance when the frequency is
50MHz?
(3) A 50kHz AC voltage with peak value of 20V is
applied to the capacitor.
1. Find the peak current
2. Find the current when the voltage is at its peak
3. Find the average power consumed by the
capacitor
4. What happens to the peak current if the frequency
becomes very high or very low?
(4) The voltage of the previous problem has the time
dependence given by
V = 20sin wt
what is the current at all times?
(5) Calculate the reactance of a 20mH inductor at a
frequency of 50kHz.
What is the reactance when the frequency is
50Hz?
What is the reactance when the frequency is
50MHz?
(6) A 50kHz AC voltage with rms value of 20V is
applied to the inductor.
1. Find the peak current
2. Find the current when the voltage is at its peak
3. Find the average power consumed.
What happens to the peak current if the frequency
becomes very high or very low?
(7) The emf of an AC power source is
ℇ = 𝟓𝟎𝒔𝒊𝒏(𝟔𝝅𝒕)
while the current is
𝑰 = 𝟐𝒔𝒊𝒏(𝟔𝝅𝒕 − 𝝅⁄𝟑)
Find the average power it delivers.
(8) Find the impedance of the combination at
frequency 60Hz.
(9) A 60Hz AC power source of 120V rms voltage is
applied to the combination of the previous problem.
Find
1. the rms current
2. the power factor
3. the average power consumed by the resistor
(10) For the circuit of the previous problem, find the
rms voltage across the resistor.
What happens to this voltage when the frequency
becomes very large?
(11)
Find the impedance of the combination:
(12) In the circuit shown, the peak voltage across
the inductor is 10V. The frequency of the AC power
source is 12kHz. Find
1. the peak voltage across the resistor
2. the peak emf
(13) Which of the following circuits is a low pass
filter?
(14) A light dimmer used to dim the stage lights in a
theater consists of a variable inductor L (whose
inductance is adjustable between zero and Lmax)
connected in series with the light bulb . The electrical
supply is 120V(rms) at 60.0Hz; the light bulb is marked
“120V,1000W”.
What Lmax is required if the rate of
energy dissipation in the light bulb
is to be varied by a factor of 5?
Assume that he resistance of the
light bulb is independent of its
temperature.