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?

(b) What is the resistance of a 150-W lightbulb?
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

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

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?

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.

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

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?

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

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

(b) the maximum current delivered by the source

(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

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?

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?

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

(b) the current in the primary

(c) the current in the secondary

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.)

(b) What is the change in frequency?

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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