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Essential University Physics

Richard Wolfson

Chapter 25

Electric Circuits - all with Video Answers

Educators

Chapter Questions

05:31

Problem 1

Are household electrical outlets connected in series or parallel? How do you know?

Manish Haldankar
Manish Haldankar
Numerade Educator
03:41

Problem 2

All the resistors in Fig. 25.24 have the same resistance. In which circuits does the battery supply the same current? (FIGURE CANT COPY)

Manish Haldankar
Manish Haldankar
Numerade Educator
03:14

Problem 3

Can the voltage across a battery's terminals differ from the battery's rated voltage? Explain.

Manish Haldankar
Manish Haldankar
Numerade Educator
03:32

Problem 4

Can the voltage across a battery's terminals be higher than the battery's rated voltage? Explain.

Manish Haldankar
Manish Haldankar
Numerade Educator
02:29

Problem 5

In some cities, streetlights are wired in such a way that when one burns out, they all go out. Are the lights in series or parallel?

Manish Haldankar
Manish Haldankar
Numerade Educator
02:25

Problem 6

When the switch in Fig. 25.25 is open, what's the voltage across the resistor? Across the switch?(FIGURE CANT COPY)

Manish Haldankar
Manish Haldankar
Numerade Educator
03:18

Problem 7

Two identical resistors in series dissipate equal power. How can this be, when electric charge loses energy in flowing through the first resistor?

Manish Haldankar
Manish Haldankar
Numerade Educator
03:40

Problem 8

When a large electric load such as a washing machine or oven comes on, lights throughout a house often dim. Why?

Manish Haldankar
Manish Haldankar
Numerade Educator
04:34

Problem 9

How would you connect a pair of equal resistors across an ideal battery in order to get the greatest power dissipation?

Manish Haldankar
Manish Haldankar
Numerade Educator
02:49

Problem 10

You have a battery whose voltage and internal resistance are unknown. Using an ideal voltmeter and an ideal ammeter, how would you determine each of these characteristics?

Manish Haldankar
Manish Haldankar
Numerade Educator
01:44

Problem 11

A student who's confused about voltage and current hooks a nearly ideal ammeter across a car battery. What happens?

AK
Akshay Kumar Khandelwal
Numerade Educator
02:11

Problem 12

A student who's confused about voltage and current tries to measure the voltage across a lighted lightbulb by inserting a voltmeter in series with the bulb. What happens to the bulb? Explain.

AK
Akshay Kumar Khandelwal
Numerade Educator
01:00

Problem 13

Sketch a circuit diagram for a circuit that includes a resistor $R_{\square}$ connected to the positive terminal of a battery, a pair of paralle resistors $R_{2}$ and $R_{3}$ connected to the lower-voltage end of $R_{1}$ and then returned to the battery's negative terminal, and a capacitor across $R_{2}$

Mirza Aslam Beig
Mirza Aslam Beig
Numerade Educator
01:28

Problem 14

Sketch a diagram for a circuit consisting of two batteries, a resistor, and a capacitor, all in series. Does the circuit description allow you any flexibility?

Manish Haldankar
Manish Haldankar
Numerade Educator
01:44

Problem 15

Resistors $R_{1}$ and $R_{2}$ are in series, and the series combination is in parallel with $R_{3} .$ This parallel combination is connected across a battery. Draw a diagram of this circuit.

Melissa T
Melissa T
Numerade Educator
01:33

Problem 16

What's the emf of a battery that delivers $27 \mathrm{J}$ of energy as it moves 3.0 C between its terminals?

Luis Rios
Luis Rios
Numerade Educator
02:52

Problem 17

A 1.5 -V battery stores $4.5 \mathrm{kJ}$ of energy. How long can it light a flashlight bulb that draws $0.60 \mathrm{A} ?$

Vishal Gupta
Vishal Gupta
Numerade Educator
01:14

Problem 18

If you accidentally leave your car headlights (current 5 A) on for an hour, how much energy drains from the car's $12-\mathrm{V}$ battery?

Narayan Hari
Narayan Hari
Numerade Educator
03:06

Problem 19

A $47-\mathrm{k} \Omega$ resistor and a $39-\mathrm{k} \Omega$ resistor are in parallel, and the pair is in series with a $22-\mathrm{k} \Omega$ resistor. What's the resistance of the combination?

Manish Haldankar
Manish Haldankar
Numerade Educator
03:51

Problem 20

What resistance should you place in parallel with a $56-\mathrm{k} \Omega$ resistor to make an equivalent resistance of $45 \mathrm{k} \Omega ?$

Manish Haldankar
Manish Haldankar
Numerade Educator
03:38

Problem 21

A defective starter motor draws 300 A from a car's 12 -V battery, dropping the battery terminal voltage to 6 V. A good starter should draw only 100 A. What will the battery terminal voltage be with a good starter?

Manish Haldankar
Manish Haldankar
Numerade Educator
02:05

Problem 22

Find the internal resistance of the battery in Exercise $21 .$

Manish Haldankar
Manish Haldankar
Numerade Educator
02:22

Problem 23

When a $9-\mathrm{V}$ battery is temporarily short-circuited, a $200-\mathrm{mA}$ current flows. What's the battery's internal resistance?

Manish Haldankar
Manish Haldankar
Numerade Educator
07:21

Problem 24

You have a $1.0-\Omega,$ a $2.0-\Omega,$ and a $3.0-\Omega$ resistor. What equivalent resistances can you form using all three?

Manish Haldankar
Manish Haldankar
Numerade Educator
06:10

Problem 25

Find all three currents in the circuit of Fig. $25.13,$ but now with $\mathcal{E}_{2}=1.0 \mathrm{V}$

Manish Haldankar
Manish Haldankar
Numerade Educator
02:48

Problem 26

What's the current through the $3-\Omega$ resistor in Fig. $25.26 ?$ (Hint:
This is trivial. Can you see why?) (FIGURE CANT COPY)

Manish Haldankar
Manish Haldankar
Numerade Educator
04:51

Problem 27

Find $I_{2}$ in Example 25.4 for the case $\mathcal{E}_{2}=2.0 \mathrm{V}$

Manish Haldankar
Manish Haldankar
Numerade Educator
03:41

Problem 28

A voltmeter with $200-\mathrm{k} \Omega$ resistance is used to measure the voltage across the $10-\mathrm{k} \Omega$ resistor in Fig. $25.27 .$ By what percentage is the measurement in error because of the finite meter resistance? (FIGURE CANT COPY)

Luis Rios
Luis Rios
Numerade Educator
02:30

Problem 29

An ammeter with $100-\Omega$ resistance is inserted in the circuit of Fig. $25.27 .$ By what percentage is the measured current in error because of the nonzero meter resistance?

Luis Rios
Luis Rios
Numerade Educator
01:31

Problem 30

A new mechanic foolishly connects an ammeter with $0.1-\Omega$ resistance directly across a $12-\mathrm{V}$ car battery with internal resistance $0.01 \Omega .$ What's the power dissipation in the meter? (No wonder it gets destroyed!)

AK
Akshay Kumar Khandelwal
Numerade Educator
03:14

Problem 31

Show that the quantity $R C$ has the units of time (seconds).

Manish Haldankar
Manish Haldankar
Numerade Educator
05:01

Problem 32

If capacitance is in $\mu \mathrm{F}$, what will be the units of the time constant
$R C$ when resistance is in (a) $\Omega,$ (b) $\mathrm{k} \Omega,$ and $(\mathrm{c})$ M\Omega? (Your answers eliminate the need for tedious power-of-10 conversions.)

Manish Haldankar
Manish Haldankar
Numerade Educator
01:57

Problem 33

Show that a capacitor is charged to approximately $99 \%$ of the applied voltage in five time constants $(5 R C)$

AK
Akshay Kumar Khandelwal
Numerade Educator
02:24

Problem 34

An uncharged $10-\mu \mathrm{F}$ capacitor and a $470-\mathrm{k} \Omega$ resistor are in series, and $250 \mathrm{V}$ is applied across the combination. How long does it take the capacitor voltage to reach $200 \mathrm{V} ?$

AK
Akshay Kumar Khandelwal
Numerade Educator
01:27

Problem 35

Find an expression for the voltage across the capacitor in Example 25.6 when it's fully charged.

AK
Akshay Kumar Khandelwal
Numerade Educator
04:00

Problem 36

In Fig. $25.28,$ all resistors have the same value, $R .$ What will be the resistance measured (a) between $A$ and $B$ or (b) between $A$ and $C ?$ (FIGURE CANT COPY)

Suman Saurav Thakur
Suman Saurav Thakur
Numerade Educator
04:44

Problem 37

In Fig. $25.28,$ take all resistors to be $1 \mathrm{k} \Omega .$ Find the current in the vertical resistor when a $6.0-\mathrm{V}$ battery is connected between $A$ and $B$ (FIGURE CANT COPY)

AK
Akshay Kumar Khandelwal
Numerade Educator
04:42

Problem 38

Three $1.5-\mathrm{V}$ batteries, with internal resistances $0.01 \Omega, 0.1 \Omega$ and $1 \Omega$, each have $1-\Omega$ resistors connected across their terminals. What's the voltage between each battery's terminals, to three significant figures?

AK
Akshay Kumar Khandelwal
Numerade Educator
01:24

Problem 39

A partially discharged car battery can be modeled as a $9-\mathrm{V}$ emf in series with a $0.08-\Omega$ internal resistance. Jumper cables connect this battery to a fully charged battery, modeled as a $12-\mathrm{V}$ emf in series with a $0.02-\Omega$ internal resistance. The cables connect $+$ to $+$ and $-$ to $-.$ What current flows through the discharged battery?

Luis Rios
Luis Rios
Numerade Educator
02:55

Problem 40

Your company is overstocked on $50-\Omega, \frac{1}{2}-$ W resistors. Your project requires $50-\Omega$ resistors that can be safely connected across a 12-V power source. How many of the available resistors will you need, and how will you connect them?

Luis Rios
Luis Rios
Numerade Educator
01:07

Problem 41

A $6.0-\mathrm{V}$ battery has internal resistance $2.5 \Omega .$ If the battery is short-circuited, what's the rate of energy dissipation in its internal resistance?

Luis Rios
Luis Rios
Numerade Educator
01:31

Problem 42

How many $100-\mathrm{W}, 120-\mathrm{V}$ lightbulbs can be connected in parallel before they trip a 20 -A circuit breaker?

Luis Rios
Luis Rios
Numerade Educator
02:25

Problem 43

You company is designing a battery-based backup power source,
In and your job is to assess its safety. You know that under damp or sweaty conditions, the resistance between two points of unbroken skin on the human body can be as low as $500 \Omega$. Your product uses
a $72-\mathrm{V}$ battery whose internal resistance is $100 \Omega .$ Is it capable of passing a fatal 100 mA (Table 24.3 ) through a damp human body?

Prashant Bana
Prashant Bana
Numerade Educator
02:51

Problem 44

Take $\mathcal{E}=12 \mathrm{V}$ and $R_{1}=270 \Omega$ in Fig. $25.4 .$ (a) What's the resistance $R_{2}$ if there's $4.5 \mathrm{V}$ across it? (b) What will be the power dissipation in $R_{2} ?$

Luis Rios
Luis Rios
Numerade Educator
05:51

Problem 45

In Fig. $25.29, R_{1}$ is a variable resistor and the other two resistors have equal resistances $R$. (a) Find an expression for the voltage across $R_{1},$ and (b) sketch a graph of this voltage as $R_{1}$ varies from
0 to $10 R$ (FIGURE CANT COPY)

Narayan Hari
Narayan Hari
Numerade Educator
04:37

Problem 46

In the circuit of Fig. $25.30,$ find (a) the current supplied by the battery and (b) the current through the $6-\Omega$ resistor. (FIGURE CANT COPY)

Luis Rios
Luis Rios
Numerade Educator
02:50

Problem 47

In Fig. $25.30,$ how much power is dissipated in the $4-\Omega$ resistor?(FIGURE CANT COPY)

Salamat Ali
Salamat Ali
Numerade Educator
04:27

Problem 48

What's the ammeter reading in Fig. $25.31 ?$ (FIGURE CANT COPY)

Luis Rios
Luis Rios
Numerade Educator
08:31

Problem 50

Find all three currents in the circuit of Fig. 25.13 with the values given, but with battery $\mathcal{E}_{2}$ reversed.

Luis Rios
Luis Rios
Numerade Educator
08:54

Problem 51

The voltage across the $30-\mathrm{k} \Omega$ resistor in Fig. 25.33 is measured with (a) a $50-\mathrm{k} \Omega$ voltmeter, (b) a $250-\mathrm{k} \Omega$ voltmeter, and (c) a 10-M\Omega digital meter. What does each read, to two significant figures?

Luis Rios
Luis Rios
Numerade Educator
08:54

Problem 51

The voltage across the $30-\mathrm{k} \Omega$ resistor in Fig. 25.33 is measured with (a) a $50-\mathrm{k} \Omega$ voltmeter, (b) a $250-\mathrm{k} \Omega$ voltmeter, and (c) a 10-M\Omega digital meter. What does each read, to two significant figures? (FIGURE CANT COPY)

Luis Rios
Luis Rios
Numerade Educator
02:35

Problem 52

In Fig. $25.34,$ what are the meter readings when an ideal (a) voltmeter or (b) ammeter is connected between $A$ and $B ?$(FIGURE CANT COPY)

Luis Rios
Luis Rios
Numerade Educator
02:43

Problem 53

A resistor draws $1.00 \mathrm{A}$ from an ideal $12.0-\mathrm{V}$ battery. (a) If an ammeter with $0.10-\Omega$ resistance is inserted in the circuit, what will it read? (b) If this current is used to calculate the resistance, by what percent will the result be in error?

Luis Rios
Luis Rios
Numerade Educator
07:34

Problem 54

The voltage across a charging capacitor in an $R C$ circuit rises to
$1-1 / e$ of the battery voltage in $5.0 \mathrm{ms}$. (a) How long will it take to reach $1-1 / e^{3}$ of the battery voltage? (b) If the capacitor is charging through a $22-\mathrm{k} \Omega$ resistor, what's the capacitance?

Luis Rios
Luis Rios
Numerade Educator
02:26

Problem 55

You're designing an external defibrillator that discharges a capacitor through the patient's body, providing a pulse that stops ventricular fibrillation. Specifications call for a capacitor storing 250 J of energy; when discharged through a body with $40-\Omega$ transthoracic resistance, the capacitor voltage is to drop to half its initial value in $10 \mathrm{ms}$. Determine the capacitance (to the nearest $10 \mu \mathrm{F})$ and initial capacitor voltage (to the nearest $100 \mathrm{V}$ ) that meet these specs.

Narayan Hari
Narayan Hari
Numerade Educator
03:40

Problem 56

A capacitor used to provide steady voltages in the power supply of a stereo amplifier charges rapidly to $35 \mathrm{V}$ every $1 / 60$ second. It must then hold that voltage to within $1.0 \mathrm{V}$ for the next $1 / 60 \mathrm{s}$ while it discharges through the amplifier. If the amplifier draws
1.2 A from the $35-\mathrm{V}$ supply, (a) what's its effective resistance, and (b) what capacitance is needed?

Luis Rios
Luis Rios
Numerade Educator
03:43

Problem 57

A capacitor is charged until it holds $5.0 \mathrm{J}$ of energy, then connected across a $10-\mathrm{k} \Omega$ resistor. In $8.6 \mathrm{ms}$, the resistor dissipates 2.0 J. Find the capacitance.

Luis Rios
Luis Rios
Numerade Educator
03:54

Problem 58

In Fig. 25.35 the $2.0-\mu \mathrm{F}$ capacitor is charged to $150 \mathrm{V}$, while the 1.0-\muF capacitor is initially uncharged. Switch $S$ is then closed. Find the total energy dissipated in the resistor as the circuit comes to equilibrium. (Hint: Think about charge conservation.) (FIGURE CANT COPY)

Ajay Singhal
Ajay Singhal
Numerade Educator
07:09

Problem 59

For the circuit of Example $25.6,$ take $\mathcal{E}=100 \mathrm{V}, R_{1}=4.0 \mathrm{k} \Omega$ and $R_{2}=6.0 \mathrm{k} \Omega,$ and assume the capacitor is initially uncharged. Find the capacitor voltage and the currents in both resistors (a) just after the switch is closed, and (b) a long time after the switch is closed. Long after the switch is closed it's reopened. What are $V_{\mathrm{C}}, I_{1},$ and $I_{2}$ (c) just after this switch opening,
and ime later?

Eduard Sanchez
Eduard Sanchez
Numerade Educator
02:30

Problem 60

In Fig. $25.36,$ the switch is initially open and both capacitors are initially uncharged. All resistors have the same value $R .$ Find expressions for the current in $R_{2}$ (a) just after the switch is closed, and (b) a long time after the switch is closed. (FIGURE CANT COPY)

Luis Rios
Luis Rios
Numerade Educator
04:39

Problem 61

A battery's voltage is measured as $4.36 \mathrm{V}$ with a voltmeter whose resistance is $1000 \Omega .$ When measured with a $1500-\Omega$ meter, it's 4.41 V. Find (a) the battery's voltage and (b) its internal resistance.

Manish Haldankar
Manish Haldankar
Numerade Educator
02:48

Problem 62

Suppose the currents into and out of a circuit node differ by 1 $\mu$ A. If the node consists of a small metal sphere with diameter $1 \mathrm{mm},$ how long would it take for the electric field around the node to reach the 3 -MV/m breakdown field in air?

Luis Rios
Luis Rios
Numerade Educator
02:48

Problem 63

Suppose the currents into and out of a circuit node differ by 1 $\mu$ A. If the node consists of a small metal sphere with diameter $1 \mathrm{mm},$ how long would it take for the electric field around the down field in air?

Luis Rios
Luis Rios
Numerade Educator
01:57

Problem 64

Show that a battery delivers the most power when the load resistance across its terminals is equal to its internal resistance. (This is not the way to treat a battery, but it's the basis for load matching in amplifiers; see Problem $65 .$ )

Luis Rios
Luis Rios
Numerade Educator
04:02

Problem 65

You're writing the instruction manual for a stereo amplifier with a maximum output of 100 W. The amplifier can be modeled as an emf in series with an $8-\Omega$ resistance. What should you specify for the loudspeaker resistance to be used with the amplifier? How much power can the amplifier deliver to a speaker with half the optimum resistance?

Luis Rios
Luis Rios
Numerade Educator
06:02

Problem 66

Show that only half the total energy drawn from a battery in charging an $R C$ circuit ends up stored in the capacitor. (Hint:
What happens to the rest? You'll need to integrate.)

Suman Saurav Thakur
Suman Saurav Thakur
Numerade Educator
03:14

Problem 67

Find the equivalent resistance between $A$ and $B$ for the circuits in Fig. 25.37 (FIGURE CANT COPY)

Luis Rios
Luis Rios
Numerade Educator
02:48

Problem 68

A $50-\Omega$ resistor is connected across a battery, and a $26-\mathrm{mA}$ current flows. When the resistor is replaced with a $22-\Omega$ resistor,
43 mA flows. Find the battery's voltage and internal resistance.

Sheh Lit Chang
Sheh Lit Chang
University of Washington
03:33

Problem 69

Obtain an expression for the rate of increase ( $d V / d t$ ) of the voltage across a charging capacitor in an $R C$ circuit. Evaluate your result at time $t=0,$ and show that if the capacitor continued charging steadily at this rate, it would reach full charge in exactly one time constant.

Luis Rios
Luis Rios
Numerade Educator
01:27

Problem 70

The circuit in Fig. 25.38 extends forever to the right, and all the resistors have the same value $R$. Show that the equivalent resistance measured across the two terminals at left is $R(1+\sqrt{5}) / 2$ (Hint: You don't need to sum an infinite series.) (FIGURE CANT COPY)

Joseph Liao
Joseph Liao
Numerade Educator
04:45

Problem 71

Figure 25.39 shows the voltage across a capacitor that's charging through a $4700-\Omega$ resistor in the circuit of Fig. $25.18 .$ Use the graph to determine (a) the battery voltage, (b) the time constant, and (c) the capacitance.(FIGURE CANT COPY)

Luis Rios
Luis Rios
Numerade Educator
10:31

Problem 72

Figure 25.40 shows a portion of a circuit used to model muscle cells and neurons. All resistors have the same value $R=1.5 \mathrm{M} \Omega$ and the emfs are $\mathcal{E}_{1}=75 \mathrm{mV}, \mathcal{E}_{2}=45 \mathrm{mV},$ and $\mathcal{E}_{3}=20 \mathrm{mV}$
Find the current through $\mathcal{E}_{3}$, including its direction.(FIGURE CANT COPY)

Luis Rios
Luis Rios
Numerade Educator
04:32

Problem 73

An electrochemical impulse traveling along the cell modeled in Fig. 25.40 changes the value of $\mathcal{E}_{3}$ so now it supplies a 40 -nA upward current. Assuming the rest of the circuit remains as described in Problem $72,$ what's the new value of $\mathcal{E}_{3} ?$

Aadit Sharma
Aadit Sharma
Numerade Educator
03:22

Problem 74

A parallel-plate capacitor has plates of area $10 \mathrm{cm}^{2}$ separated by a 0.10 -mm layer of glass insulation with resistivity $\rho=1.2 \times 10^{13} \Omega \cdot \mathrm{m}$ and dielectric constant $\kappa=5.6 .$ Because of the finite resistivity, charge leaks through the insulation. (a) How can such a leaky capacitor be represented in a circuit diagram?
(b) Find the time constant for this capacitor to discharge through its insulation, and show that it depends only on the properties of the insulating material and not on its dimensions.

Vishal Gupta
Vishal Gupta
Numerade Educator
01:36

Problem 75

Write the node and loop equations for the circuit in Fig. $25.23 a$ (Example 25.6 ), and find the time constant.

Dominador Tan
Dominador Tan
Numerade Educator
01:32

Problem 76

In Problem $60,$ take $C_{1}=C_{2}=C,$ and find the current through $R_{2}$ as a function of time. (Hint: Use the node and loop laws to get a differential equation for the current, and use the initial conditions on current and its derivative to evaluate the constants of integration.)

Manik Pulyani
Manik Pulyani
Numerade Educator
01:07

Problem 77

You're about to purchase a battery. Normally, batteries are rated in ampere-hours- - the total charge they can deliver. Your application calls for a 5 - A -h battery. But the 6 -V battery you see while shopping online is rated at 50 watt-hours. Will it work?

Luis Rios
Luis Rios
Numerade Educator
00:49

Problem 78

Stray voltage is a serious problem on dairy farms, often resulting from corroded wiring or poor wiring practices. These conditions can produce several volts between the ground and metal watering bowls, feed troughs, or milking equipment. Cows feel shocks that make them nervous, reducing milk output and sometimes leading to mammary gland infections. As a result, farmers can face serious financial losses. Figure 25.41 shows a typical stray-voltage situation, with the source of stray voltage modeled as a $6-\mathrm{V}$ emf in series with a $1-\mathrm{k} \Omega$ resistance. (FIGURE CANT COPY)
The current through the $500-\Omega$ cow will be
a. $3 \mathrm{mA}$
b. $4 \mathrm{mA}$
c. $6 \mathrm{mA}$
d. $12 \mathrm{mA}$

Luis Rios
Luis Rios
Numerade Educator
00:52

Problem 79

Stray voltage is a serious problem on dairy farms, often resulting from corroded wiring or poor wiring practices. These conditions can produce several volts between the ground and metal watering bowls, feed troughs, or milking equipment. Cows feel shocks that make them nervous, reducing milk output and sometimes leading to mammary gland infections. As a result, farmers can face serious financial losses. Figure 25.41 shows a typical stray-voltage situation, with the source of stray voltage modeled as a $6-\mathrm{V}$ emf in series with a $1-\mathrm{k} \Omega$ resistance. (FIGURE CANT COPY)
The voltage across the cow shown is
a. $2 \mathrm{V}$
b. $4 \mathrm{V}$
c. $6 \mathrm{V}$
d. nearly 0 V.

Luis Rios
Luis Rios
Numerade Educator
00:30

Problem 80

Stray voltage is a serious problem on dairy farms, often resulting from corroded wiring or poor wiring practices. These conditions can produce several volts between the ground and metal watering bowls, feed troughs, or milking equipment. Cows feel shocks that make them nervous, reducing milk output and sometimes leading to mammary gland infections. As a result, farmers can face serious financial losses. Figure 25.41 shows a typical stray-voltage situation, with the source of stray voltage modeled as a $6-\mathrm{V}$ emf in series with a $1-\mathrm{k} \Omega$ resistance. (FIGURE CANT COPY)
In an effort to diagnose the problem, a farmer connects an ideal voltmeter between the water bowl and ground, with the cow absent. The voltmeter reading is
a. $2 \mathrm{V}$
b. $4 \mathrm{V}$
c. $6 \mathrm{V}$
d. none of the above.

Luis Rios
Luis Rios
Numerade Educator
00:46

Problem 81

Stray voltage is a serious problem on dairy farms, often resulting from corroded wiring or poor wiring practices. These conditions can produce several volts between the ground and metal watering bowls, feed troughs, or milking equipment. Cows feel shocks that make them nervous, reducing milk output and sometimes leading to mammary gland infections. As a result, farmers can face serious financial losses. Figure 25.41 shows a typical stray-voltage situation, with the source of stray voltage modeled as a $6-\mathrm{V}$ emf in series with a $1-\mathrm{k} \Omega$ resistance. (FIGURE CANT COPY)
To explore the problem further, a farmer connects an ideal ammeter between the water bowl and ground, with the cow absent. The ammeter reading is
a. $4 \mathrm{mA}$
b. $6 \mathrm{mA}$
c. $12 \mathrm{mA}$
d. infinite.

Luis Rios
Luis Rios
Numerade Educator