27 February 2014

Physics Homework Chapter 21


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1. (a) What is the resistance of a lightbulb that uses an average power of 60.0 W when connected to a 60.0-Hz power source having a maximum voltage of 128 V?
_____Ω

(b) What is the resistance of a 150-W lightbulb?
_____Ω
Calculator Problem 1

Calculator Problem #1

(Calculate Resistance)
Pav1 = Watts
ΔVmax = V
Pav2 Watts

R1 Ω
R2 Ω




2. The figure below shows three lamps connected to a 120-V AC (rms) household supply voltage. Lamps 1 and 2 have 120-W bulbs; lamp 3 has a 40.0-W bulb.

(a) For each bulb, find the rms current.
Irms, lamp 1  =_____A
Irms, lamp 2  =_____A
Irms, lamp 3  =_____A

(b) For each bulb, find the resistance.
Rlamp 1  =_____Ω
Rlamp 2  =_____Ω
Rlamp 3  =_____Ω





3. What is the maximum current delivered to a circuit containing a 1.40 µF capacitor when it is connected across the following outlets?

(a) a North American outlet having ΔVrms = 120 V, f = 60.0 Hz
_____mA

(b) a European outlet having ΔVrms = 240 V and f = 50.0 Hz
_____mA





4. What maximum current is delivered by an AC source with ΔVmax = 56.4 V and f = 79.4 Hz when connected across a 3.70-µF capacitor?
_____mA

Chapter 21 Problem #4

Chapter 21 Problem 4

(Calculate Current)
Vmax V
f Hz
C μF

I mA;




5. In a purely inductive AC circuit as shown in the figure, ΔVmax = 100 V.

(a) The maximum current is 3.80 A at 40.0 Hz. Calculate the inductance L.
_____mH

(b) At what angular frequency ω is the maximum current 1.90 A?
_____rad/s




6. A sinusoidal voltage Δv = (60 V) sin (190t) is applied to a series RLC circuit with L = 90 mH, C = 165 μF, and R = 46 Ω.

(a) What is the impedance of the circuit?
____Ω

(b) What is the maximum current in the circuit?
_____A





7. A resistor (R = 900 Ω), a capacitor (C = 0.25 µF), and an inductor (L = 2.5 H) are connected in series across a 240 Hz AC source for which ΔVmax = 135 V. Calculate the following.
(a) the impedance of the circuit
_____Ω

(b) the maximum current delivered by the source
_____A

(c) the phase angle between the current and voltage
_____°
(d) Is the current leading or lagging behind the voltage?
-The current leads the voltage.
-There is no phase difference between the current and voltage.  
-The current lags behind the voltage.




8. A multimeter in an RL circuit records an rms current of 0.600 A and a 65.0 Hz rms generator voltage of 105 V. A wattmeter shows that the average power delivered to the resistor is 10.0 W. Determine values for the following:

(a) the impedance in the circuit
_____ ohms

(b) the resistance, R
_____ ohms

(c) the inductance, L
_____H



9. A series RLC circuit has a resistance of 10 Ω and an impedance of 70 Ω. If the rms voltage applied to the circuit is 140 V, what average power is delivered to the circuit?
_____W




10.The primary coil of a transformer has N1 = 2.00  102 turns, and its secondary coil has N2 = 4.00  102 turns. If the input voltage across the primary coil is Δv = (180 V) sin ωt, what rms voltage is developed across the secondary coil?
_____V




11. A transformer on a pole near a factory steps the voltage down from 3600 V (rms) to 120 V (rms). The transformer is to deliver 1900 kW to the factory at 90% efficiency. Find values for the following.

(a) the power delivered to the primary
_____kW

(b) the current in the primary
_____A

(c) the current in the secondary
_____A




12. A spaceship is approaching a space station at a speed of 3.45  105 m/s. The space station has a beacon that emits green light with a frequency of 5.97  1014 Hz.

(a) What is the frequency of the beacon observed on the spaceship? (Carry five digits in these calculations. Use c = 2.9979  108 m/s for the speed of light. State your answer to five significant figures.)
_____Hz

(b) What is the change in frequency?
_____Hz


Chapter 21 Problem #12

Chapter 21 Problem 12

(Calculate Observed Frequency)
v m/s
fs Hz
c m/s

fo Hz
Δf Hz



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