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Introductory Circuit Analysis

Robert L. Boylestad

Chapter 4

Ohm's Law, Power, and Energy - all with Video Answers

Educators

Chapter Questions

01:04

Problem 1

What is the voltage across a $47 \Omega$ resistor if the current through it is $2.5 \mathrm{~A}$ ?

Vishal Gupta
Vishal Gupta
Numerade Educator
01:52

Problem 2

What is the current through a $6.8 \Omega$ resistor if the voltage drop across it is $12 \mathrm{~V}$ ?

Manish Kumar
Manish Kumar
Numerade Educator
00:57

Problem 3

How much resistance is required to limit the current to $1.5 \mathrm{~mA}$ if the potential drop across the resistor is $6 \mathrm{~V}$ ?

Nishant Kumar
Nishant Kumar
Numerade Educator
00:59

Problem 4

At starting, what is the current drain on a $12 \mathrm{~V}$ car battery if the resistance of the starting motor is $40 \mathrm{M} \Omega$ ?

Ajay Singhal
Ajay Singhal
Numerade Educator
01:10

Problem 5

If the current through a $0.02 \mathrm{M} \Omega$ resistor is $3.6 \mu \mathrm{A}$, what is the voltage drop across the resistor?

Prabhat Tyagi
Prabhat Tyagi
Numerade Educator
01:36

Problem 6

If a voltmeter has an internal resistance of $15 \mathrm{k} \Omega$, find the current through the meter when it reads $62 \mathrm{~V}$.

Varsha Aggarwal
Varsha Aggarwal
Numerade Educator
01:27

Problem 7

If a refrigerator draws $2.2 \mathrm{~A}$ at $120 \mathrm{~V}$, what is its resistance?

Vishal Gupta
Vishal Gupta
Numerade Educator
03:49

Problem 8

If a clock has an internal resistance of $7.5 \mathrm{k} \Omega$, find the current through the clock if it is plugged into a $120 \mathrm{~V}$ outlet.

Vishal Gupta
Vishal Gupta
Numerade Educator
01:17

Problem 9

A washing machine is rated at $4.2 \mathrm{~A}$ at $120 \mathrm{~V}$. What is its internal resistance?

Vishal Gupta
Vishal Gupta
Numerade Educator
00:42

Problem 10

A CD player draws $125 \mathrm{~mA}$ when $4.5 \mathrm{~V}$ is applied. What is the internal resistance?

Mrinal Rana
Mrinal Rana
Numerade Educator
01:01

Problem 11

The input current to a transistor is $20 \mu \mathrm{A}$. If the applied (input) voltage is $24 \mathrm{mV}$, determine the input resistance of the transistor.

Jacob Shpiece
Jacob Shpiece
Numerade Educator
01:39

Problem 12

The internal resistance of a dc generator is $0.5 \Omega$. Determine the loss in terminal voltage across this internal resistance if the current is $15 \mathrm{~A}$.

Shahab Ullah
Shahab Ullah
Numerade Educator
05:09

Problem 13

a. If an electric heater draws $9.5 \mathrm{~A}$ when connected to a $120 \mathrm{~V}$ supply, what is the internal resistance of the heater?
b. Using the basic relationships of Chapter 2, how much energy is converted in $1 \mathrm{~h}$ ?

Yaqub Khan
Yaqub Khan
Numerade Educator
01:04

Problem 14

In a TV camera, a current of $2.4 \mu \mathrm{A}$ passes through a resistor of $3.3 \mathrm{M} \Omega$. What is the voltage drop across the resistor?

Vishal Gupta
Vishal Gupta
Numerade Educator
03:19

Problem 15

a. Plot the curve of $I$ (vertical axis) versus $V$ (horizontal axis) for a $120 \Omega$ resistor. Use a horizontal scale of 0 to $100 \mathrm{~V}$ and a vertical scale of 0 to $1 \mathrm{~A}$.
b. Using the graph of part (a), find the current at a voltage of $20 \mathrm{~V}$ and $50 \mathrm{~V}$.

Rashmi Sinha
Rashmi Sinha
Numerade Educator
03:16

Problem 16

a. Plot the $I-V$ curve for a $5 \Omega$ and a $20 \Omega$ resistor on the same graph. Use a horizontal scale of 0 to $40 \mathrm{~V}$ and a vertical scale of 0 to $2 \mathrm{~A}$.
b. Which is the steeper curve? Can you offer any general conclusions based on results?
c. If the horizontal and vertical scales were interchanged, which would be the steeper curve?

Khoobchandra Agrawal
Khoobchandra Agrawal
Numerade Educator
00:30

Problem 17

. a. Plot the $I-V$ characteristics of a $1 \Omega, 100 \Omega$, and $1000 \Omega$ resistor on the same graph. Use a horizontal axis of 0 to $100 \mathrm{~V}$ and a vertical axis of 0 to $100 \mathrm{~A}$.
b. Comment on the steepness of a curve with increasing levels of resistance.

Dading Chen
Dading Chen
Numerade Educator
01:35

Problem 18

Sketch the internal resistance characteristics of a device that has an internal resistance of $20 \Omega$ from 0 to $10 \mathrm{~V}$, an internal resistance of $4 \Omega$ from $10 \mathrm{~V}$ to $15 \mathrm{~V}$, and an internal resistance of $1 \Omega$ for any voltage greater than $15 \mathrm{~V}$. Use a horizontal scale that extends from 0 to $20 \mathrm{~V}$ and a vertical scale that permits plotting the current for all values of voltage from 0 to $20 \mathrm{~V}$.

Shoukat Ali
Shoukat Ali
Other Schools
03:16

Problem 19

a. Plot the $I-V$ characteristics of a $2 \mathrm{k} \Omega, 1 \mathrm{M} \Omega$, and a $100 \Omega$ resistor on the same graph. Use a horizontal axis of 0 to $20 \mathrm{~V}$ and a vertical axis of 0 to $10 \mathrm{~mA}$.
b. Comment on the steepness of the curve with decreasing levels of resistance.
c. Are the curves linear or nonlinear? Why?

Khoobchandra Agrawal
Khoobchandra Agrawal
Numerade Educator

Problem 20

If $420 \mathrm{~J}$ of energy are absorbed by a resistor in $4 \mathrm{~min}$, what is the power to the resistor?

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01:20

Problem 21

The power to a device is 40 joules per second (J/s). How long will it take to deliver $640 \mathrm{~J}$ ?

Rachel B.
Rachel B.
Numerade Educator
02:31

Problem 22

a. How many joules of energy does a $2 \mathrm{~W}$ nightlight dissipate in $8 \mathrm{~h}$ ?
b. How many kilowatthours does it dissipate?

Hubert Agamasu
Hubert Agamasu
Numerade Educator
02:09

Problem 23

A resistor of $10 \Omega$ has charge flowing through it at the rate of 300 coulombs per minute ( $\mathrm{C} / \mathrm{min}$ ). How much power is dissipated?

Km Neeraj
Km Neeraj
Numerade Educator
01:21

Problem 24

How long must a steady current of $1.4 \mathrm{~A}$ exist in a resistor that has $3 \mathrm{~V}$ across it to dissipate $12 \mathrm{~J}$ of energy?

Mark Scythian
Mark Scythian
Numerade Educator
01:13

Problem 25

What is the power delivered by a $6 \mathrm{~V}$ battery if the charge flows at the rate of $48 \mathrm{C} / \mathrm{min}$ ?

Nishant Kumar
Nishant Kumar
Numerade Educator

Problem 26

The current through a $4 \mathrm{k} \Omega$ resistor is $7.2 \mathrm{~mA}$. What is the power delivered to the resistor?

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01:23

Problem 27

The power consumed by a $2.2 \mathrm{k} \Omega$ resistor is $240 \mathrm{~mW}$. What is the current level through the resistor?

Vishal Gupta
Vishal Gupta
Numerade Educator
03:20

Problem 28

What is the maximum permissible current in a $120 \Omega, 2 \mathrm{~W}$ resistor? What is the maximum voltage that can be applied across the resistor?

Shahab Ullah
Shahab Ullah
Numerade Educator
01:16

Problem 29

The voltage drop across a transistor network is $12 \mathrm{~V}$. If the total resistance is $5.6 \mathrm{k} \Omega$, what is the current level? What is the power delivered? How much energy is dissipated in $1 \mathrm{~h}$ ?

Chai Santi
Chai Santi
Numerade Educator
01:36

Problem 30

If the power applied to a system is $324 \mathrm{~W}$, what is the voltage across the line if the current is $2.7 \mathrm{~A}$ ?

Thomas Thompson
Thomas Thompson
Numerade Educator
01:02

Problem 31

A $1 \mathrm{~W}$ resistor has a resistance of $4.7 \mathrm{M} \Omega$. What is the maximum current level for the resistor? If the wattage rating is increased to $2 \mathrm{~W}$, will the current rating double?

Sheh Lit Chang
Sheh Lit Chang
University of Washington
01:30

Problem 32

A $2.2 \mathrm{k} \Omega$ resistor in a stereo system dissipates $42 \mathrm{~mW}$ of power. What is the voltage across the resistor?

Vishal Gupta
Vishal Gupta
Numerade Educator
02:44

Problem 33

A dc battery can deliver $45 \mathrm{~mA}$ at $9 \mathrm{~V}$. What is the power rating?

Vishal Gupta
Vishal Gupta
Numerade Educator
01:06

Problem 34

What are the "hot" resistance level and current rating of a $120 \mathrm{~V}, 100 \mathrm{~W}$ bulb?

Sheh Lit Chang
Sheh Lit Chang
University of Washington
02:31

Problem 35

What are the internal resistance and voltage rating of a $450 \mathrm{~W}$ automatic washer that draws $3.75 \mathrm{~A}$ ?

CG
Coleman Green
Numerade Educator
05:50

Problem 36

A calculator with an internal $3 \mathrm{~V}$ battery draws $0.4 \mathrm{~mW}$ when fully functional.
a. What is the current demand from the supply?
b. If the calculator is rated to operate $500 \mathrm{~h}$ on the same battery, what is the ampere-hour rating of the battery?

Rashmi Sinha
Rashmi Sinha
Numerade Educator
03:20

Problem 37

A $20 \mathrm{k} \Omega$ resistor has a rating of $100 \mathrm{~W}$. What are the maximum current and the maximum voltage that can be applied to the resistor?

Shahab Ullah
Shahab Ullah
Numerade Educator
01:44

Problem 38

A $10 \Omega$ resistor is connected across a $12 \mathrm{~V}$ battery.
a. How many joules of energy will it dissipate in $1 \mathrm{~min}$ ?
b. If the resistor is left connected for $2 \mathrm{~min}$ instead of $1 \mathrm{~min}$, will the energy used increase? Will the power dissipation level increase?

Vishal Gupta
Vishal Gupta
Numerade Educator
02:01

Problem 39

How much energy in kilowatthours is required to keep a $230 \mathrm{~W}$ oil-burner motor running $12 \mathrm{~h}$ a week for 5 months? (Use $4 / /$ weeks $=1$ month.)

Mayukh Banik
Mayukh Banik
Numerade Educator
02:10

Problem 40

How long can a $1500 \mathrm{~W}$ heater be on before using more than $12 \mathrm{kWh}$ of energy?

Vishal Gupta
Vishal Gupta
Numerade Educator
02:36

Problem 41

How much does it cost to use a $24 \mathrm{~W}$ radio for $3 \mathrm{~h}$ at $9 \mathrm{e}$ per kilowatthour?

Vishal Gupta
Vishal Gupta
Numerade Educator
02:21

Problem 42

a. In $10 \mathrm{~h}$ an electrical system converts $1200 \mathrm{kWh}$ of electrical energy into heat. What is the power level of the system?
b. If the applied voltage is $208 \mathrm{~V}$, what is the current drawn from the supply?
c. If the efficiency of the system is $82 \%$, how much energy is lost or stored in $10 \mathrm{~h}$ ?

Surjit Tewari
Surjit Tewari
Numerade Educator
02:44

Problem 43

At 9 per kilowatthour, how long can you play a $250 \mathrm{~W}$ color television for $\$ 1$ ?

Vishal Gupta
Vishal Gupta
Numerade Educator
01:20

Problem 44

A $60 \mathrm{~W}$ bulb is on for one hour. Find the energy converted in
a. watthours
b. wattseconds
c. joules
d. kilowatthours

Morgan Cheatham
Morgan Cheatham
Numerade Educator
02:20

Problem 45

A small, portable black-and-white television draws $0.455 \mathrm{~A}$ at $9 \mathrm{~V}$.
a. What is the power rating of the television?
b. What is the internal resistance of the television?
c. What is the energy converted in $6 \mathrm{~h}$ of typical battery life?

Sheh Lit Chang
Sheh Lit Chang
University of Washington
14:04

Problem 46

a. If a house is supplied with $120 \mathrm{~V}, 100 \mathrm{~A}$ service, find the maximum power capability.
b. Can the homeowner safely operate the following loads at the same time?
$5 \mathrm{hp}$ motor
$3000 \mathrm{~W}$ clothes dryer
$2400 \mathrm{~W}$ electric range
$1000 \mathrm{~W}$ steam iron
c. If all the appliances are used for 2 hours, how much energy is converted in $\mathrm{kWh}$ ?

Ryan Kutayiah
Ryan Kutayiah
Texas A&M University
03:48

Problem 47

What is the total cost of using the following at $9 \notin$ per kilowatthour?
a. $860 \mathrm{~W}$ air conditioner for $6 \mathrm{~h}$
b. $4800 \mathrm{~W}$ clothes dryer for $30 \mathrm{~min}$
c. $900 \mathrm{~W}$ coffee maker for $20 \mathrm{~min}$
d. $110 \mathrm{~W}$ stereo for $3.5 \mathrm{~h}$

Shoukat Ali
Shoukat Ali
Other Schools
04:27

Problem 48

What is the total cost of using the following at $9 \notin$ per kilowatthour?
a. $200 \mathrm{~W}$ fan for $4 \mathrm{~h}$
b. $1200 \mathrm{~W}$ dryer for $20 \mathrm{~min}$
c. $70 \mathrm{~W}$ radio for $1.5 \mathrm{~h}$
d. $150 \mathrm{~W}$ color television set for $2 \mathrm{~h} 10 \mathrm{~min}$

Vidhi Bhatt
Vidhi Bhatt
Numerade Educator
02:26

Problem 49

What is the efficiency of a motor that has an output of $0.5 \mathrm{hp}$ with an input of $395 \mathrm{~W}$ ?

Km Neeraj
Km Neeraj
Numerade Educator
00:44

Problem 50

The motor of a power saw is rated $68.5 \%$ efficient. If $1.8 \mathrm{hp}$ are required to cut a particular piece of lumber, what is the current drawn from a $120 \mathrm{~V}$ supply?

Mayukh Banik
Mayukh Banik
Numerade Educator
00:52

Problem 51

What is the efficiency of a dryer motor that delivers $1 \mathrm{hp}$ when the input current and voltage are $4 \mathrm{~A}$ and $220 \mathrm{~V}$, respectively?

Varsha Aggarwal
Varsha Aggarwal
Numerade Educator
02:42

Problem 52

A stereo system draws $2.4 \mathrm{~A}$ at $120 \mathrm{~V}$. The audio output power is $50 \mathrm{~W}$.
a. How much power is lost in the form of heat in the system?
b. What is the efficiency of the system?

Averell Hause
Averell Hause
Carnegie Mellon University
01:09

Problem 53

If an electric motor having an efficiency of $76 \%$ and operating off a $220 \mathrm{~V}$ line delivers $3.6 \mathrm{hp}$, what input current does the motor draw?

Narayan Hari
Narayan Hari
Numerade Educator
02:19

Problem 54

A motor is rated to deliver $2 \mathrm{hp}$.
a. If it runs on $110 \mathrm{~V}$ and is $90 \%$ efficient, how many watts does it draw from the power line?
b. What is the input current?
c. What is the input current if the motor is only $70 \%$ efficient?

Kayla Gephart
Kayla Gephart
Numerade Educator
02:28

Problem 55

An electric motor used in an elevator system has an efficiency of $90 \%$. If the input voltage is $220 \mathrm{~V}$, what is the input current when the motor is delivering $15 \mathrm{hp}$ ?

Sheh Lit Chang
Sheh Lit Chang
University of Washington
01:03

Problem 56

The motor used on a conveyor belt is $85 \%$ efficient. If the overall efficiency is $75 \%$, what is the efficiency of the conveyor belt assembly?

Narendra Kumar
Narendra Kumar
Numerade Educator
02:26

Problem 57

A $2 \mathrm{hp}$ motor drives a sanding belt. If the efficiency of the motor is $87 \%$ and that of the sanding belt is $75 \%$ due to slippage, what is the overall efficiency of the system?

Km Neeraj
Km Neeraj
Numerade Educator
01:18

Problem 58

If two systems in cascade each have an efficiency of $80 \%$ and the input energy is $60 \mathrm{~J}$, what is the output energy?

Jayashree Behera
Jayashree Behera
Numerade Educator
01:21

Problem 59

The overall efficiency of two systems in cascade is $72 \%$. If the efficiency of one is 0.9 , what is the efficiency in percent of the other?

A M
A M
Numerade Educator

Problem 60

a. What is the total efficiency of three systems in cascade with efficiencies of $98 \%, 87 \%$, and $21 \%$ ?
b. If the system with the least efficiency ( $21 \%$ ) were removed and replaced by one with an efficiency of $90 \%$, what would be the percentage increase in total efficiency?

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03:56

Problem 61

If the total input and output power of two systems in cascade are $400 \mathrm{~W}$ and $128 \mathrm{~W}$, respectively, what is the efficiency of each system if one has twice the efficiency of the other?

Narayan Hari
Narayan Hari
Numerade Educator
02:57

Problem 62

. Using PSpice or Multisim, repeat the analysis of the circuit in Fig. 4.26 with $E=400 \mathrm{mV}$ and $R=0.04 \mathrm{M} \Omega$.

Kajal Gautam
Kajal Gautam
Numerade Educator

Problem 63

Using PSpice or Multisim, repeat the analysis of the circuit in Fig. 4.26, but reverse the polarity of the battery and use $E=0.02 \mathrm{~V}$ and $R=240 \Omega$.

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