Wall Socket 120V HOT NEUTRAL R1 1400 Fan Motor MotorWindings 210 MechanicalWork 52V HeatingCoil1 $500 HeatingCoil2 210 S1

Introductory Circuit Analysis (13th Edition)
13th Edition
ISBN:9780133923605
Author:Robert L. Boylestad
Publisher:Robert L. Boylestad
Chapter1: Introduction
Section: Chapter Questions
Problem 1P: Visit your local library (at school or home) and describe the extent to which it provides literature...
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4.
Preface: For this problem we are assuming the voltages are constant
(also known as "de" voltages). This isn't actually the case, but, we will later learn that you
can treat alternating voltages (such as would actually exist in this scenario) by appropriately
scaled constant voltages.
Hair dryers have a small motor that runs a fan, plus two heating coils for making the air
hot enough to dry hair. The circuit diagram below depicts a hair dryer on the right side
(everything to the right of the nodes labeled HOT and NEUTRAL) and it is receiving power
by being plugged into a wall socket that provides 120 V (as depicted to the left). One of the
heating coils can be switched in or out of operation via the switch S1 shown in the circuit.
The resistor R1 ensure that the motor is not damaged by excessive voltage. Note that the
model of the motor is a voltage “source” in series with a resistor, but this source will only
consume power.
(a) Will the dryer produce more hot air when the switch S1 is open or closed? Justify your
answer. (Resistors produce heat proportional to the power they are dissipating.)
(b) Find the Thévenin equivalent of the whole hair dryer (everything to the right of the
HOT and NEUTRAL nodes), in the state where the switch S1 is closed. (The closed
switch merely acts as a typical wire.)
(c) Let us consider the current that the hair dryer draws. What is the current that is drawn
from the wall socket using the full Thévenin model? Also, what is the current that is
drawn if we ignore the Thévenin voltage and assume the dryer can be modeled solely by
its Thévenin resistance? (Hint: You should find that there isn't a significant difference
in these currents and hence it is typically reasonable to approximate a hair dryer as just
a resistor.)
Wall Socket
120V
HOT
NEUTRAL
R1
1400
Fan Motor
MotorWindings
210
MechanicalWork
52V
HeatingCoil1
$500
HeatingCoil2
210
S1
Transcribed Image Text:4. Preface: For this problem we are assuming the voltages are constant (also known as "de" voltages). This isn't actually the case, but, we will later learn that you can treat alternating voltages (such as would actually exist in this scenario) by appropriately scaled constant voltages. Hair dryers have a small motor that runs a fan, plus two heating coils for making the air hot enough to dry hair. The circuit diagram below depicts a hair dryer on the right side (everything to the right of the nodes labeled HOT and NEUTRAL) and it is receiving power by being plugged into a wall socket that provides 120 V (as depicted to the left). One of the heating coils can be switched in or out of operation via the switch S1 shown in the circuit. The resistor R1 ensure that the motor is not damaged by excessive voltage. Note that the model of the motor is a voltage “source” in series with a resistor, but this source will only consume power. (a) Will the dryer produce more hot air when the switch S1 is open or closed? Justify your answer. (Resistors produce heat proportional to the power they are dissipating.) (b) Find the Thévenin equivalent of the whole hair dryer (everything to the right of the HOT and NEUTRAL nodes), in the state where the switch S1 is closed. (The closed switch merely acts as a typical wire.) (c) Let us consider the current that the hair dryer draws. What is the current that is drawn from the wall socket using the full Thévenin model? Also, what is the current that is drawn if we ignore the Thévenin voltage and assume the dryer can be modeled solely by its Thévenin resistance? (Hint: You should find that there isn't a significant difference in these currents and hence it is typically reasonable to approximate a hair dryer as just a resistor.) Wall Socket 120V HOT NEUTRAL R1 1400 Fan Motor MotorWindings 210 MechanicalWork 52V HeatingCoil1 $500 HeatingCoil2 210 S1
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A hair dryer circuit with input voltage of 120 volts.

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