Chapter 21 Solutions Directed Reading for Content Mastery

Mastering Physics Solutions Chapter 21 Electric Electric current and Straight-Current Circuits

Mastering Physics Solutions

Affiliate 21 Electric current and Direct-Current Circuits Q.1CQ
What is the direction of the electric current produced by an electron that falls toward the ground?
Solution:
By convention, the direction of electric current is always in the contrary direction to the motion of negative charge. If the electron falls toward the ground. then the direction of electric current is in the upward management

Chapter 21 Current and Direct-Electric current Circuits Q.1P
How many coulombs of charge are in i ampere-hour?
Solution:

Chapter 21 Electric current and Direct-Current Circuits Q.2CQ
Your trunk is composed of electric charges Does it follow, then, that you produce an electric current when you walk?
Solution:
No An electric electric current ¡due south proc1ucei when a internet charge mores Your trunk is electrically neutral, so no current is produced when you walk

Chapter 21 Electric Current and Straight-Current Circuits Q.2P
A flashlight bulb carries a current of 0.eighteen A for 78 due south. How much charge flows through the seedling in this time? How many electrons?
Solution:

Chapter 21 Electric Electric current and Direct-Electric current Circuits Q.3CQ
Suppose you charge a rummage by rubbing it through your pilus Do you produce a current when you walk across the room carrying the rummage?
Solution:
No.
By rubbing the comb through your hair you have transferred charge from your pilus to the comb but the net accuse of you and the comb together is however zero Therefore no current is produced when you walk beyond the room carrying the comb

Chapter 21 Electrical Electric current and Direct-Current Circuits Q.3P
The picture tube in a particular television draws a current of fifteen A. How many electrons strike the viewing screen every 2d?
Solution:

Affiliate 21 Electric Current and Direct-Electric current Circuits Q.4CQ
Suppose you charge a rummage by rubbing t through the fur on your dog's back Practice you lot produce a current when you walk across the room carrying the comb?
Solution:
Yes
There is a cyberspace accuse separated and deposited on the rummage surface and by moving the comb one place to another you have created an electric current

Chapter 21 Electrical Current and Direct-Current Circuits Q.4P
IP A car bombardment does 260 J of work on the charge passing through it as it starts an engine,
(a) If the emf of the battery is 12 V, how much charge passes through the battery during the beginning?
(b) If the emf is doubled to 24 V, does the amoun,t of accuse passing through the battery increment or decrease? By what factor?
Solution:

Chapter 21 Electric Electric current and Direct-Current Circuits Q.5CQ
An electron moving through a wire has an average drift speed that is very small Does this mean that its instantaneous velocity is also very minor?
Solution:
No.
An electron may have a fairly large instant velocity at any given fourth dimension Only considering its direction of motion keeps changing due to its collisions with atoms in the wire its average velocity in particular direction is almost very very small.

Chapter 21 Electric Current and Direct-Current Circuits Q.5P
Highly sensitive ammeters can measure out currents as small every bit ten.0 fA. How many electrons per second menses through a wire with a 10.0-fA current?
Solution:

Chapter 21 Electric Current and Directly-Current Circuits Q.6CQ
Arc car headlights connected in series or parallel? Give an everyday observation that supports your answer
Solution:
Car head lights are wired in parallel as we can tell by the fact that some intendance has just one working caput light.

Chapter 21 Current and Direct-Electric current Circuits Q.6P
A idiot box set continued to a 120-Five outlet consumes 78 Westward of power, (a) How much electric current flows through the television receiver? (b) How long does it take for ten million electrons to pass through the TV?
Solution:

Affiliate 21 Electric current and Direct-Electric current Circuits Q.7CQ
Requite an case of how four resistors of resistance R can be combined to produce an equivalent resistance of R.
Solution:

Affiliate 21 Electrical Current and Direct-Current Circuits Q.7P
BIO Pacemaker Batteries Pacemakers designed for longterm use commonly employ a lithium-iodine bombardment capable of
supplying 0.42 A · h of charge,
(a) How many coulombs of charge can such a battery supply?
(b) If the average current produced by the pacemaker is v.6 μ A, what is the expected lifetime of the device?
Solution:

Affiliate 21 Electric Current and Direct-Electric current Circuits Q.8CQ
Is information technology possible to connect a group of resistors of value R in such a way that the equivalent resistance is less than R? If so, give a specific example.
Solution:

Chapter 21 Electric Current and Directly-Electric current Circuits Q.8P
CE A conducting wire is quadrupled in length and tripled in bore,
(a) Does its resistance increase, decrease, or stay the same? Explain,
(b) By what gene does its resistance change?
Solution:

Chapter 21 Electric Electric current and Straight-Current Circuits Q.9CQ
What physical quantity practise resistors connected in serial accept in common?
Solution:

Chapter 21 Electric current and Direct-Current Circuits Q.9P

Solution:

Affiliate 21 Electric Current and Direct-Current Circuits Q.10CQ
What physical quantity exercise resistors connected in parallel accept in mutual?
Solution:

Chapter 21 Electric Current and Directly-Current Circuits Q.10P
Current-versus-voltage plots for ii materials, A and B, are shown in Figure 21-26.
(a) Is the resistance of material A greater than, less than, or equal to the resistance of cloth B at the voltage V1?
(b) Cull the best explanation from amid the following:
I. Curve B is higher in value than bend A.
II. A larger slope ways a larger value of I/5, and hcnce a smaller value of R.
3. Curve B has the larger gradient at the voltage V1 and hence the larger resistance.
Solution:

Chapter 21 Electrical Current and Direct-Electric current Circuits Q.11CQ
Explain how electric devices tin begin operating almost immediately later y'all throw a switch. even though individual electrons in the wire may take hours to reach the device
Solution:
Each electron in the wire affects its neighbors by means of electrical field exerting a force on them causing them to move
Thus when electrons begin to move out of a battery their motion sets up a propagating influence that moves through the wire at nearly the speed of light causing electrons everywhere in the wire to begin moving.
In this way electrical device tin begin operating nigh immediately after we throw a switch even though individual electrons in the wire may take hours to reach the device

Chapter 21 Current and Direct-Current Circuits Q.11P
Two cylindrical wires are made of the same fabric and accept the aforementioned length. If wire B is to have nine times the resistance of wire A, what must be the ratio of their radii, rB/rA?
Solution:

Affiliate 21 Electric Current and Direct-Electric current Circuits Q.12CQ
Explain the difference between resistivity and resistance.
Solution:

Chapter 21 Electric Electric current and Direct-Electric current Circuits Q.12P
A silver wire is 5.9 thou long and 0.49 mm in bore. What is its resistance?
Solution:

Affiliate 21 Electric Current and Straight-Current Circuits Q.13CQ
Explain why birds can roost on high-voltage wire without being electrocuted
Solution:
A number of factors come into play hera
—t Outset the bottom of a bird'south human foot is tough and definitely not a good usher of electricity.
—, Secondly the potential departure is required for the flow of current thru the bird's body. contact with a high voltage wire isn't enough to cause a problem. in that location demand a contact with a lower voltage Source
Only the bird is in contact with essentially the same high voltage in two different places (Where its two feet impact the wire) which doesn't lead to a potential difference The but potential departure the bird feel is due to the very small voltage drib along the segment of wire between the bird's two feet

Affiliate 21 Electric Electric current and Straight-Current Circuits Q.13P
When a potential deviation of 18 5 is practical to a given wire, it conducts 0.35 A of current. What is the resistance of the wire?
Solution:

Chapter 21 Electric Current and Direct-Current Circuits Q.14CQ
List two electrical applications that would benefit from room-temperature superconductors. List two applications for which room-temperature superconductivity would not be beneficial.
Solution:
Magnetic resonance imaging (MRI) machines would definitely benefit from room temperature super conductivity
As it is. they must absurd their magnets to law temperature Similarly.
Electric power transmission would benefit if the resistance of the wires could be eliminated On the other manus, a toaster or an electrical oven requires resistance to do its task: super conductivity would not assist

Chapter 21 Electrical Current and Direct-Current Circuits Q.14P
The tungsten filament of a lightbulb has a resistance of 0.07 Ω. If the filament is 27 cm long, what is its diameter?
Solution:

Chapter 21 Electric Current and Direct-Current Circuits Q.15CQ
Oil what bones conservation laws are Kirchhoffs rules based?
Solution:
The junction dominion is based on conservation of electric charge the loop rule is based on the conservation energy

Chapter 21 Electrical Current and Direct-Electric current Circuits Q.15P
What is the resistance of vi.0 mi of copper wire with a diameter of 0.55 mm?
Solution:

Chapter 21 Electrical Current and Direct-Current Circuits Q.16CQ
What physical quantity exercise capacitors connected in series accept in common?
Solution:
Consider some capacitors connected in series with a battery The plate of the capacitor which is connected to the positive end of the battery volition acquire positive charge and this will crusade
same amount of negative charge to develop at the other negative plate of the capacitor The negative accuse volition then cause the capacitor adjacent to it to develop same corporeality of charge- In this way all the capacitors in the series connexion will get same amount of charga Hence, in a serial connection, the physical quantity that the capacitors take in mutual is the electric charge

Affiliate 21 Electrical Current and Directly-Current Circuits Q.16P

Solution:

Chapter 21 Electric Electric current and Direct-Current Circuits Q.17CQ
What physical quantity exercise capacitors continued in parallel have in common?
Solution:
When the capacitors are connected in parallel and then the potential deviation is the mutual quantity on all the capacitors.

Affiliate 21 Electric Electric current and Direct-Current Circuits Q.17P
IP A bird lands on a bare copper wire carrying a current of 32 A. The wire is viii estimate, which means that its cantankerous-exclusive area is 0.13 cm2,
(a) Find the difference in potential between the bird's feet, assuming they are separated by a altitude of half dozen.0 cm.
(b) Will your answer to part (a) increase or subtract if the separation between the bird'due south feet increases? Explicate.
Solution:

Chapter 21 Electric Current and Straight-Current Circuits Q.18CQ

Solution:

Chapter 21 Electric Current and Direct-Current Circuits Q.18P
A current of 0.96 A flows through a copper wire 0.44 mm in diameter when it is connected to a potential deviation of xv Five. How long is the wire?
Solution:

Chapter 21 Electric Current and Direct-Current Circuits Q.19P
IP BIO Electric current Through a Jail cell Membrane A typical cell membrane is 8.0 nm thick and has an electrical resistivity of ane.3 × 107 Ω · m.
(a) If the potential difference between the inner and outer surfaces of a jail cell membrane is 75 mV, how much current flows through a square area of membrane ane.0 μ m on a side?
(b) Suppose the thickness of the membrane is doubled,
merely the resistivity and potential departure remain the aforementioned. Does the current increase or subtract? By what factor?
Solution:

Chapter 21 Electric Current and Direct-Current Circuits Q.20P
When a potential divergence of 12 V is applied to a wire 6.nine m long and 0.33 mm in bore, the result is an current of 2.1 A. What is the resistivity of the wire?
Solution:

Affiliate 21 Electric Current and Straight-Electric current Circuits Q.21P
IP
(a) What is the resistance per meter of an aluminum wire with a cross-sectional expanse of ii.4 × ten-vii m2.
(b) Would your answer to part (a) increase, decrease, or stay the same if the diameter of the wire were increased? Explain,
(c) Repeat role (a) for a wire with a cross-sectional area of 3.half-dozen × 10−7 m2.
Solution:

Chapter 21 Electric Current and Direct-Current Circuits Q.22P
BIO Resistance and Current in the Human Finger The interior of the human being body has an electrical resistivity of 0.xv Ω · m.
(a) Guess the resistance for electric current flowing the length of your index finger. (For this calculation, ignore the much college resistivity of your pare.)
(b) Your muscles will contract when they carry a current greater than xv mA. What voltage is required to produce this current through your finger?
Solution:

Chapter 21 Electric Current and Direct-Current Circuits Q.23P
CE Calorie-free A has four times the ability rating of calorie-free B when operated at the same voltage,
(a) Is the resistance of light A greater than, less than, or equal to the resistance of low-cal B? Explain,
(b) What is the ratio of the resistance of light A to the resistance of light B?
Solution:

Chapter 21 Electric Current and Straight-Current Circuits Q.24P
CE Light A has four times the power rating of light B when operated at the same voltage.
(a) Is the resistance of light A greater than, less than, or equal to the resistance of light B? Explain.
(b) What is the ratio of the resistance of light A to the resistance of light B?
Solution:

Chapter 21 Electric Electric current and Direct-Current Circuits Q.25P
CE Two lightbulbs operate on the aforementioned potential departure. Bulb Ahas four times the power output of bulb B.
(a) Which seedling has the greater current passing through information technology? Explain,
(b) What is the ratio of the current in bulb A to the current in seedling B?
Solution:
Given that,
Ii calorie-free bulbs operate on the same potential difference. Bulb 'A' has 4 times the power output of bulb B.
(a) In terms of potential deviation 'Five' and current 'I', the power output of the bulbs tin can be written as
P = I V
Information technology is given that 'V' is the same for both bulbs.
It follows, then, that the current in bulb 'A' is greater than the current in bulb 'B'
(b) Since ability is proportional to electric current, the current in bulb 'A' is four times greater than the current in bulb B.

Affiliate 21 Electric current and Direct-Current Circuits Q.26P
CE 2 lightbulbs operate on the same current. Bulb A has 4 times the power output of bulb B.
(a) Is the potential divergence beyond bulb A greater than or less than the potential difference across bulb B? Explain,
(b) What is the ratio of the potential difference beyond bulb A to that across seedling B?
Solution:
Given that,
Two light bulbs operate on the same current; Bulb 'A' has 4 times the ability output of bulb 'B'.
(a) In terms of potential departure 'Five' and current 'I', the power output of the bulbs can be written as
P = I V
Information technology is given that electric current 'I' is same for both bulbs.
It follows, that the potential difference in bulb 'A' is greater than the potential difference in seedling 'B'.
(b) Since power is proportional to potential difference, the potential divergence in seedling 'A' is four times greater than the potential difference in bulb 'B'.
Chapter 21 Electric Current and Direct-Current Circuits Q.27P
A 75-Five generator supplies 3.8 kW of power. How much current does the generator produce?
Solution:

Chapter 21 Electric Current and Direct-Current Circuits Q.28P
A portable CD thespian operates with a electric current of 22 mA at a potential divergence of 4.1 5. What is the power usage of the thespian?
Solution:

Chapter 21 Electric Current and Direct-Current Circuits Q.29P
Find the power dissipated in a 25-Ω electric heater connected to a 120-V outlet.
Solution:

Chapter 21 Electric Current and Straight-Electric current Circuits Q.30P
The electric current in a 120-V reading lamp is two.6 A. If the toll of electrical energy is $0.075 per kilowatt-hour, how much does it cost to operate the light for
Solution:

Chapter 21 Electric Electric current and Direct-Current Circuits Q.31P
Information technology costs two.6 cents to charge a automobile bombardment at a voltage of 12 V and a current of 15 A for 120 minutes. What is the cost of electrical free energy per kilowatt-hour at this location?
Solution:

Chapter 21 Current and Direct-Current Circuits Q.32P
IP A 75-W lightbulb operates on a potential difference of 95 Five. Find
(a) the electric current in the bulb and
(b) the resistance of the bulb,
(c) If this bulb is replaced with 1 whose resistance is half the value establish in part
(b), is its ability rating greater than or less than 75 W? By what gene?
Solution:

Chapter 21 Electric Electric current and Directly-Electric current Circuits Q.33P
Rating Auto Batteries Car batteries are rated by the post-obit two numbers:
(1) cranking amps = current the battery can produce for 30.0 seconds while maintaining a final voltage of at least 7.2 V and
(ii) reserve capacity = number of minutes the battery can produce a 25-A current while maintaining a terminal voltage of at least x.5 V. Ane item battery is advertised as having 905 cranking amps and a 155-minute reserve capacity. Which of these two ratings represents the greater amount of free energy delivered by the battery?
Solution:

Chapter 21 Electric current and Direct-Electric current Circuits Q.34P
CE Predict/Explicate A dozen identical lightbulbs are connected to a given emf.
(a) Will the lights be brighter if they are connected in series or in parallel?
(b) Cull the all-time explanation from among the following:
I. When continued in parallel each seedling experiences the maximum emf and dissipates the maximum power.
2. Resistors in serial accept a larger equivalent resistance and dissipate more power.
Iii. Resistors in parallel have a smaller equivalent resistance and dissipate less power.
Solution:

Chapter 21 Electrical Current and Direct-Current Circuits Q.35P
CE Predict/Explain A fuse is a device to protect a circuit from the effects of a large current. The fuse is a pocket-size strip of metal that burns through when the current in it exceeds a certain value, thus producing an open up circuit,
(a) Should a fuse be connected in serial or in parallel with the circuit it is intended to protect?
(b) Choose the best caption from among the following:
I. Either connection is acceptable; the primary tiling is to accept a fuse in the circuit.
II. The fuse should exist connected in parallel, otherwise it volition interrupt the current in the excursion.
3. With the fuse connected in series, the current in the circuit drops to naught every bit soon equally the fuse bruns through.
Solution:
(a) Fuse should exist always connected in series.
If the fuse is connected in series, when the fuse is blown out it makes an open up excursion and the appliances are protected from high current.
(b) If the fuse is connected in series and when the fuse is blown it becomes an open circuit and the current in the excursion becomes nothing.
Hence best explanation is III

Affiliate 21 Electric Electric current and Direct-Current Circuits Q.36P
CE A circuit consists of three resistors, R123, connected in series to a battery. Rank these resistors in gild of increasing
(a) current through them and
(b) potential difference across them. Indicate ties where appropriate.
Solution:

Chapter 21 Electrical Current and Straight-Current Circuits Q.37P
CE Predict/Explain Two resistors are connected in parallel,
(a) If a third resistor is now connected in parallel with the original two, does the equivalent resistance of the excursion increase, decrease, or remain the same?
(b) Choose the best explanation from amid the following:
I. Calculation a resistor generally tends to increase the resistance, but putting it in parallel tends to decrease the resistance; therefore the furnishings kickoff and the resistance stays the same.
2. Adding more than resistance to the excursion volition increase the equivalent resistance.
III. The third resistor gives however another path for current to flow in the circuit, which means that the equivalent resistance is less.
Solution:

Affiliate 21 Electrical Current and Straight-Current Circuits Q.38P

Solution:
The equivalent resistance (R) of the resistors which are connected in series is equal to the sum of the resistance of the private resistors.

Chapter 21 Electric Current and Direct-Current Circuits Q.39P
What is the minimum number of 65-Ω resistors that must exist connected in parallel to produce an equivalent resistance of 11 Ω or less?
Solution:

Chapter 21 Electric Electric current and Direct-Current Circuits Q.40P

Solution:

Chapter 21 Electric Current and Directly-Current Circuits Q.41P
Your toaster has a power cord with a resistance of 0.020 Ω connected in series with a 9.6-Ω nichrome heating element. If the potential difference between the terminals of the toaster is 120 5, how much ability is dissipated in
(a) the power cord and
(b) the heating element?
Solution:

Affiliate 21 Current and Direct-Current Circuits Q.42P
A hobbyist building a radio needs a 150-Ω resistor in her circuit, but has only a 220-Ω, a 79-Ω, and a 92-Ω resistor available. How tin can she connect these resistors to produce the desired resistance?
Solution:

Chapter 21 Electric Current and Direct-Electric current Circuits Q.43P
A circuit consists of a 12.0-V bombardment connected to three resistors (42 Ω, 17 Ω, and 110 Ω) in series. Find
(a) the current that flows through the battery and
(b) the potential difference across each resistor.
Solution:

Chapter 21 Electric Electric current and Directly-Electric current Circuits Q.44P
IP Three resistors, xi Ω, 53 Ω, and R, are connected in serial with a 24.0-V battery. The total current flowing through the battery is 0.16 A.
(a) Find the value of resistance R.
(b) Find the potential deviation beyond each resistor,
(c) If the voltage of the battery had been greater than 24.0 V, would your answer to office (a) have been larger or smaller? Explicate.
Solution:

Chapter 21 Electric Current and Directly-Current Circuits Q.45P
A circuit consists of a bombardment continued to 3 resistors (65 Ω, 25 Ω, and 170 Ω) in parallel. The full electric current through the resistors is ane.8 A. Find
(a) the emf of the bombardment and
(b) the current through each resistor.
Solution:

Chapter 21 Current and Straight-Electric current Circuits Q.46P
IP 3 resistors, 22 Ω, 67 Ω, and R, are connected in parallel with a 12.0-V battery. The total electric current flowing through the battery is 0.88 A.
(a) Find the value of resistance R.
(b) Find the electric current through each resistor,
(c) If the full current in the battery had been greater than 0.88 A, would your answer to role (a) have been larger or smaller? Explicate.
Solution:

Chapter 21 Electric Current and Direct-Current Circuits Q.47P
An 89-Ω resistor has a electric current of 0.72 A and is connected in series with a 130-Ω resistor. What is the emf of the bombardment to wliich the resistors are connected?
Solution:

Chapter 21 Electrical Current and Straight-Current Circuits Q.48P

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Chapter 21 Electrical Current and Direct-Current Circuits Q.49P

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Chapter 21 Electrical Current and Direct-Current Circuits Q.50P
How many 65-W lightbulbs can be continued m parallel across a potential difference of 85 V earlier the full current in the circuit exceeds 2.1 A?
Solution:

Affiliate 21 Electric Electric current and Directly-Current Circuits Q.51P

Solution:

Affiliate 21 Electric Current and Directly-Electric current Circuits Q.52P
IP A 12-V bombardment is continued to terminals A and B in Effigy 21-30.
(a) Given that R = 85 Ω, find the current in each resistor.
(b) Suppose the value of R is increased. For each resistor in plow, state whether the current flowing through it increases or decreases. Explain.
Solution:

Chapter 21 Electric Current and Direct-Electric current Circuits Q.53P
IP The terminals A and B in Effigy 21-31 are connected to a nine.0-V battery,
(a) Detect the electric current flowing through each resistor,
(b) Is the potential difference beyond the six.3-Ω resistor greater than, less than, or the aforementioned as the potential difference beyond the 1.five-Ω resistor? Explicate.
Solution:

Chapter 21 Electric Electric current and Directly-Current Circuits Q.54P
IP Suppose the battery in Figure 21-32 has an internal resistance r = 0.25 Ω
(a) How much current flows through the battery?
(b) What is the potential difference between the terminals of the battery? (c) If the iii.2-Ω resistor is increased in value, will the current in the battery increase or subtract? Explain.
Solution:

Chapter 21 Electric Electric current and Direct-Current Circuits Q.55P

Solution:

Chapter 21 Current and Directly-Current Circuits Q.56P
The current in the 13.8-Ω resistor in Figure 21- 0.795 A. Detect the electric current in the other resistors in the excursion
Solution:

Affiliate 21 Electric Electric current and Direct-Current Circuits Q.57P

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Chapter 21 Electric Electric current and Direct-Electric current Circuits Q.58P

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Chapter 21 Electrical Electric current and Straight-Current Circuits Q.59P
IP Suppose the polarity of the 11.v-V battery in Figure 21-35 is reversed,
(a) Practise you wait this to increment or decrease the amount of current flowing in the circuit? Explain,
(b) Calculate the magnitude and management (clockwise or counterclockwise) of the current in this case.
Solution:

Chapter 21 Electrical Current and Direct-Current Circuits Q.60P
IP It is given that signal A in Effigy 21-35 is grounded (V = 0).
(a) Is the potential at bespeak B greater than or less than goose egg? Explicate,
(b) Is the potential at point C greater than or less than zero? Explain,
(c) Calculate the potential at signal D.
Solution:

Chapter 21 Electrical Current and Direct-Current Circuits Q.61P

Solution:

Chapter 21 Electrical Current and Direct-Electric current Circuits Q.62P
Suppose bespeak A is grounded (V = 0) in Figure 21-36. Find the potential at points B and C.
Solution:

Affiliate 21 Electrical Current and Direct-Current Circuits Q.63P

Solution:

Chapter 21 Electric current and Direct-Current Circuits Q.64P

Solution:

Affiliate 21 Electrical Current and Direct-Current Circuits Q.65P
CE Ii capacitors, C1 = C and C2 = 2C, are connected to a battery,
(a) Which capacitor stores more energy when they are connected to the battery in series? Explain,
(b) Which capacitor stores more energy when they are connected in parallel? Explain.
Solution:

Chapter 21 Electric Electric current and Direct-Current Circuits Q.66P
CE Predict/Explain Two capacitors are connected in series,
(a) If a third capacitor is now connected in serial with the original two, does the equivalent capacitance increment, decrease, or remain the same?
(b) Choose the best explanation from among the following:
I. Adding a capacitor more often than not tends to increase the capacitance, just putting information technology in series tends to decrease the capacitance; therefore, the net effect is no change.
Two. Adding a capacitor in serial will increase the total amount of charge stored, and hence increase the equivalent capacitance.
Iii. Calculation a capacitor in series decreases the equivalent capacitance since each capacitor now has less voltage across it, and hence stores less accuse.
Solution:

Chapter 21 Electric current and Direct-Current Circuits Q.67P
CE Predict/Explain Two capacitors are connected in parallel,
(a) If a third capacitor is at present connected in parallel with the original two, does the equivalent capacitance increase, decrease, or remain the same?
(b) Choose the best caption from among the following:
I. Adding a capacitor tends to increase the capacitance, but putting information technology in parallel tends to subtract the capacitance; therefore, the net upshot is no modify.
II. Calculation a capacitor in parallel volition increase the total amount of charge stored, and hence increase the equivalent capacitance.
III. Adding a capacitor in parallel decreases the equivalent capacitance since each capacitor now has less voltage across it, and hence stores less charge.
Solution:

Chapter 21 Current and Direct-Current Circuits Q.68P

Solution:

Chapter 21 Electric Electric current and Straight-Electric current Circuits Q.69P
A 12-Five battery is connected to iii capacitors in series. The capacitors have the following capacitances: iv.v μ F, 12 μ F, and 32 μ F. Find the voltage across the 32- μ F capacitor.
Solution:

Chapter 21 Electric Current and Direct-Current Circuits Q.70P
CE You conduct a series of experiments in which you connect the capacitors C1 and C2 > C1 to a battery in various ways. The experiments are as follows:
A, C1 alone connected to the battery;
B, C2 alone continued to the battery;
C, C1 and C2 connected to the battery in series;
D, C1 and C2 connected to the bombardment in parallel. Rank these 4 experiments in order of increasing equivalent capacitance. Indicate ties where appropriate.
Solution:
The ranking is C<A<B<D
This follows because two capacitors in series have equivalent capacitances less than the smallest of the capacitor and two capacitor connected in parallel accept an equivalent capacitance greater than the largest of the capacitors.

Chapter 21 Electric Electric current and Direct-Current Circuits Q.71P

Solution:

Chapter 21 Electric Current and Straight-Current Circuits Q.72P
Terminals A and B in Figure 21-39 are connected to a 9.0-V battery. Find the energy stored in each capacitor.
Solution:
Therefore, free energy stored incapacitor is approximately.

Chapter 21 Electrical Current and Direct-Electric current Circuits Q.73P
IP 2 capacitors, one 7.5 μ F and the other 15 μ F, are continued in parallel beyond a xv-V battery,
(a) Find the equivalent capacitance of the two capacitors,
(b) Which capacitor stores more charge? Explain,
(c) Find the accuse stored on each capacitor.
Solution:

Chapter 21 Electric Current and Straight-Current Circuits Q.74P
IP Two capacitors, one 7.5 μ F and the other 15 μ F, are connected in series across a 15-Five battery,
(a) Observe the equivalent capacitance of the two capacitors,
(b) Which capacitor stores more than accuse? Explain,
(c) Find the charge stored on each capacitor.
Solution:

Chapter 21 Electric Current and Direct-Current Circuits Q.75P

Solution:

Affiliate 21 Electric Electric current and Direct-Current Circuits Q.76P
Two capacitors, C1 and C2, are continued in series and charged by a battery. Prove that the energy stored in C1 plus the energy stored in C2 is equal to the energy stored in the equivalent capacitor, Ceq, when information technology is continued to the same bombardment.
Solution:

Chapter 21 Electric Electric current and Direct-Current Circuits Q.77P

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Affiliate 21 Electrical Current and Direct-Current Circuits Q.78P
The switch on an RC excursion is closed at t = 0. Given that ε = ix.0 Five, R = 150 Ω, and C = 23 μ F, how much accuse is on the capacitor at time t = 4.two ms?
Solution:

Chapter 21 Electric Current and Direct-Current Circuits Q.79P
ε The capacitor in an RC excursion (R = 120 Ω, C = 45 μ F) is initially uncharged. Find
(a) the accuse on the capacitor and
(b) the current in the circuit i fourth dimension constant (τ = RC) after the circuit is connected to a 9.0-5 battery.
Solution:

Chapter 21 Electric Current and Direct-Current Circuits Q.80P

Solution:

Chapter 21 Electric Electric current and Direct-Current Circuits Q.81P
Consider an RC circuit with ε = 12.0 V, R = 175 Ω, and C = 55.7 μ F. Find
(a) the time constant for the circuit,
(b) the maximum charge on the capacitor, and
(c) the initial electric current in the circuit.
Solution:

Chapter 21 Electric Current and Direct-Current Circuits Q.82P
The resistor in an RC circuit has a resistance of 145 Ω.
(a) What capacitance must be used in this excursion if the fourth dimension abiding is to be iii.5 ms?
(b) Using the capacitance adamant in role (a), calculate the current in the circuit 7.0 ms after the switch is closed. Assume that the capacitor is uncharged initially and that the emf of the battery is nine.0 V.
Solution:

Affiliate 21 Electric Current and Straight-Current Circuits Q.83P
A flash unit for a camera has a capacitance of 1500 μ F. What resistance is needed in this RC circuit if the flash is to charge to 90% of its full charge in 21 s?
Solution:

Affiliate 21 Electric Electric current and Direct-Current Circuits Q.84P

Solution:

Chapter 21 Electrical Current and Directly-Current Circuits Q.85P

Solution:

Chapter 21 Electrical Current and Direct-Current Circuits Q.86P
The capacitor in an RC excursion is initially uncharged. In terms of R and C, decide
(a) the time required for the charge on the capacitor to rising to 50% of its final value and
(b) the fourth dimension required for the initial current to drop to 10% of its initial value.
Solution:

Affiliate 21 Electrical Current and Direct-Current Circuits Q.87GP
CE A given car battery is rated every bit 250 amp-hours. Is this rating a measure of energy, power, charge, voltage, or electric current? Explicate.
Solution:

Chapter 21 Electric Current and Direct-Electric current Circuits Q.88GP
CE Predict/Explain The resistivity of tungsten increases with temperature,
(a) When a light containing a tungsten filament heats up, does its power consumption increment, decrease, or stay the same?
(b) Choose the best caption from among the following:
I. The voltage is unchanged, and therefore an increment in resistance implies a reduced power, as nosotros can run into from P = V2/R.
Ii. Increasing the resistance increases the power, as is clear from P = I2R.
III. The power consumption is contained of resistance, as we tin see from P = IV.
Solution:

Chapter 21 Electrical Current and Directly-Current Circuits Q.89GP
CE A cylindrical wire is to exist doubled in length, merely it is desired that its resistance remain the same,
(a) Must its radius exist increased or decreased? Explicate,
(b) By what factor must the radius exist changed?
Solution:

Chapter 21 Electric Current and Direct-Current Circuits Q.90GP
CE Predict/Explain An electric space heater has a power rating of 500 W when connected to a given voltage Five.
(a) If two of these heaters are connected in series to the same voltage, is the power consiuned by the two heaters greater than, less than, or equal to m W? (b) Choose the best explanation from amongst the following:
I. Each heater consumes 500 West; therefore two of them will swallow 500 W + 500 Due west = thousand W.
II. The voltage is the same, only the resistance is doubled by connecting the heaters in scries. Therefore, the power consumed (P = V2/R) is less than one thousand W.
3. Connecting two heaters in serial doubles the resistance. Since ability depends on the resistance squared, it follows that the ability consumed is greater than 1000 West.
Solution:

Chapter 21 Electric Current and Direct-Current Circuits Q.91GP
CE Two resistors, R1 = R and R2 = 2R, are connected to a bombardment.
(a) Which resistor dissipates more power when they are connected to the battery in series? Explain,
(b) Which resistor dissipates more power when they aie connected in parallel? Explicate.
Solution:

Chapter 21 Electric Electric current and Straight-Current Circuits Q.92GP

Solution:

Affiliate 21 Electric Current and Direct-Current Circuits Q.93GP
CE Predict/Explain
(a) Referring to Trouble 92 arid the circuit in Effigy 21-45, does the current supplied by the battery increase, decrease, or remain the aforementioned when the switch is closed?
(a) Cull the best explanation from among the following:
I. The electric current decreases considering only two resistors tin can draw current from the bombardment when the switch is closed.
Ii. Closing the switch makes no deviation to the electric current since the second resistor is nonetheless connected to the battery as before.
3. Closing the switch shorts out the 2d resistor, decreases the total resistance of the excursion, and increases the current.
Solution:

Chapter 21 Electric Current and Directly-Current Circuits Q.94GP
CE Predict/Explain
(a) Referring to Problem 92 and the circuit in Effigy 21-45, does the total power dissipated in the circuit increase, subtract, or remain the same when the switch is closed?
(b) Cull the all-time caption from among the post-obit:
I. Endmost the switch shorts out one of the resistors, which means that the power dissipated decreases.
2. The equivalent resistance of the circuit is reduced by endmost the switch, only the voltage remains the aforementioned. Therefore, from P = V2/R nosotros run across that the power dissipated increases.
Iii. The power dissipated remains the same considering power, P = Four, is contained of resistance.
Solution:

Affiliate 21 Electric Current and Straight-Current Circuits Q.95GP

Solution:

Chapter 21 Electric Current and Direct-Current Circuits Q.96GP
CE Predict/Explain
(a) When the switch is closed in the excursion shown in Effigy 21-46, does the current supplied by the battery increment, decrease, or stay the same?
(b) Cull the best caption from amongst the following:
I. The current increases because three resistors are cartoon current from the battery when the switch is closed, rather than just ii.
Ii. Closing the switch makes no difference to the current considering the voltage is the same equally before.
Iii. Closing the switch decreases the current considering an boosted resistor is added to the circuit.
Solution:

Chapter 21 Electric current and Direct-Current Circuits Q.97GP
CE Predict/Explain
(a) When the switch is airtight in the circuit shown in Figure 21-46, does the total power dissipated in the circuit increase, decrease, or stay the same?
(b) Choose the all-time explanation from amid the following:
I. Closing the switch adds i more resistor to the circuit This makes it harder for the bombardment to supply current which decreases the power dissipated.
Ii. The equivalent resistance of the circuit is reduced by closing the switch, but the voltage remains the same. Therefore from P = V2/R we see that the power dissipated increases
Iii. The power prodigal remains the same considering power P = Iv, is independent of resistance.
Solution:

Chapter 21 Electric Current and Direct-Electric current Circuits Q.98GP
Suppose that points A and B in Figure 21-30 are connected to a 12-Five battery. Find the power dissipated in each of the resistors assuming that R = 65 Ω.
Solution:

Chapter 21 Electric Current and Direct-Current Circuits Q.99GP
You lot are given resistors of 413 Ω, 521 Ω, and 146 Ω. Describe how these resistors must be continued to produce an equivalent resistance of 255 Ω.
Solution:

Chapter 21 Electric Current and Direct-Current Circuits Q.100GP
You lot arc given capacitors of 18 μF, 7.ii μF, and 9.0 μF. Depict how these capacitors must be connected to produce an equivalent capacitance of 22 μF.
Solution:

Chapter 21 Electric Electric current and Directly-Current Circuits Q.101GP
Suppose your automobile carries a chargc of 85 μC. What current does it produce as it travels from Dallas to Fort Worth (35 mi) in 0.75 h?
Solution:

Chapter 21 Electric Current and Direct-Current Circuits Q.102GP

Solution:

Chapter 21 Electric Current and Directly-Current Circuits Q.103GP

Solution:

Chapter 21 Electric Electric current and Direct-Current Circuits Q.104GP
It is desired to construct a 5.0-Ω resistor from a one.2-k length of tungsten wire. What diameter is needed for this wire?
Solution:

Chapter 21 Electric Current and Straight-Current Circuits Q.105GP
Electrical Safety Codes For prophylactic reasons, electrical codes have been established that limit the amount of current a wire of a given size can carry. For case, an 18-gauge (cross- sectional area = 1.17 mm2), safe-insulated extension cord with copper wires tin can carry a maximum current of v.0 A. Find the voltage drop in a 12-ft, 18-approximate extension cord carrying a electric current of 5.0 A. (Note: In an extension cord, the current must flow through two lengths—downwards and back.)
Solution:

Chapter 21 Electric Current and Direct-Current Circuits Q.106GP

Solution:

Chapter 21 Electric Current and Direct-Current Circuits Q.107GP
A portable CD histrion uses a current of 7.five mA at a potential departure of iii.5 Five.
(a) How much energy does the player use in 35 s?
(b) Suppose the role player has a mass of 0.65 kg. For what length of time could the role player operate on the energy required to lift information technology through a height of 1.0 m?
Solution:

Chapter 21 Electric Electric current and Direct-Electric current Circuits Q.108GP
An electric heating coil is immersed in 4.6 kg of h2o at 22 °C. The coil, which has a resistance of 250 Ω, warms the water to 32 °C in 15 min. What is the potential difference at
which the coil operates?
Solution:

Chapter 21 Electric current and Direct-Electric current Circuits Q.109GP

Solution:

Chapter 21 Electric current and Direct-Electric current Circuits Q.110GP
A silver wire and a copper wire take the same volume and the aforementioned resistance. Observe the ratio of their radii, r silver/r copper·
Solution:

Chapter 21 Electric Current and Direct-Current Circuits Q.111GP
2 resistors are connected in series to a battery with an emf of 12 Five. The voltage across the starting time resistor is two.7 V and the current through the second resistor is 0.15 A. Find the resistance of the 2 resistors.
Solution:

Chapter 21 Current and Directly-Electric current Circuits Q.112GP
BIOPacemaker Pulses A pacemaker sends a pulse to a patient'southward centre every time the capacitor in the pacemaker charges to a voltage of 0.25 5. Information technology is desired that the patient receive 75 pulses per minute. Given that the capacitance of the pacemaker is 110 μF and that the battery has a voltage of 9.0 Five, what value should the resistance have?
Solution:

Chapter 21 Electric Electric current and Direct-Current Circuits Q.113GP
A long, sparse wire has a resistance R. The wire is at present cut into three segments of equal length, which are connected in parallel. In terms of R, what is the equivalent resistance of the three wire segments?
Solution:

Chapter 21 Current and Direct-Electric current Circuits Q.114GP

Solution:

Chapter 21 Electric Current and Directly-Current Circuits Q.115GP
IP Suppose we connect a 12.0-V battery to terminals A and B in Figure 21-29.
(a) Is the electric current in the 45-Ω resistor greater than, less than, or the same as the electric current in the 35-Ω resistor? Explicate,
(b) Calculate the electric current flowing through each of the three resistors in this circuit.
Solution:

Affiliate 21 Electrical Current and Direct-Electric current Circuits Q.116GP
IP Suppose the battery in Figure 21-50 has an internal resistance of 0.73 Ω.
(a) What is the potential departure beyond the terminals of the battery when the switch is open?
(b) When the switch is closed, does the potential difference of the bombardment increment or subtract? Explain,
(c) Discover the potential difference beyond the bombardment after the switch has been airtight a long time.
Solution:

Chapter 21 Current and Direct-Current Circuits Q.117GP

Solution:

Chapter 21 Electrical Electric current and Direct-Current Circuits Q.118GP
IP 15.0-5 battery is connected to terminals A and B in Effigy 21-41.
(a) Given that C = fifteen.0 μF, find the accuse on each of the capacitors,
(b) Find the total free energy stored in this system,
(c) If the 7.22-μF capacitor is increased in value, will the total energy stored in the excursion increment or decrease? Explain.
Solution:

Chapter 21 Electric Current and Directly-Electric current Circuits Q.119GP
IP The switch in the RC circuit shown in Figure 21-44 is airtight at t = 0.
(a) How much power is prodigal in each resistor only after t = 0 and in the limit t → ∞?
(b) What is the charge on the capacitor at the time t = 0.35 ms?
(c) How much free energy is stored in the capacitor in the limit t → ∞??
(d) If the voltage of the bombardment is doubled, by what factor does your answer to office (c) change? Explain.
Solution:

Affiliate 21 Electric Current and Directly-Current Circuits Q.120GP
2 resistors, R1 and R2, are continued in parallel and connected to a battery. Testify that the power dissipated in R1 plus the power dissipated in R2 is equal to the power prodigal in the equivalent resistor, Req, when it is continued to the same battery.
Solution:

Chapter 21 Electric Electric current and Direct-Current Circuits Q.121GP
A bombardment has an emf ε and an internal resistance r. When the battery is continued to a 25-Ω resistor, the electric current through the bombardment is 0.65 A. When the battery is connected to a 55-Ω resistor, the electric current is 0.45 A. Find the battery's emf and internal resistance.
Solution:
Summate battery's emf and internal resistance by applying Kirchhoff's loop rule to the circuit.
Kirchhoff's loop rule states that equally ane moves around a airtight loop in a excursion, the algebraic sum of the potential difference must be zero.

Affiliate 21 Current and Direct-Electric current Circuits Q.122GP
When ii resistors, R1 and R2, are connected in series across a 6.0-V battery, the potential difference across R1 is 4.0 5. When R1 and R2 are connccted in parallel to the same battery, the current through R2 is 0.45 A. Notice the values of R1 and R2.
Solution:

Chapter 21 Electric Current and Direct-Electric current Circuits Q.123GP
Suppose the voltmeter measures a potential difference of 3.70 5 across the resistor. What is the current that flows through the person'southward torso?
A. 3.70 × x-6A
B. 5.00 × 10-5A
C. 0.0740 A
D. three.70 A
Solution:

Affiliate 21 Electrical Electric current and Straight-Electric current Circuits Q.124PP
What is the resistance of the person and footwear when the voltmeter reads 3.70 V?
A. 1.25 × 107Ω
B. 1.35 × 107 Ω
C. 4.63 × 107 Ω
D. 1.71 × 108 Ω
Solution:

Chapter 21 Electric Current and Direct-Electric current Circuits Q.125PP
The resistance of a given person and footwear is 4.00 × 107Ω What is the reading on the voltmeter when this person is tested?
A. 0.976 5
B. 1.22 V
C. 1.25 V
D. 50.0 V
Solution:

Chapter 21 Electric Current and Directly-Electric current Circuits Q.126PP
The resistance of a given person and footwear is 4.00 × 107Ω What is the reading on the voltmeter when this person is tested?
A. 0.976 V
B. 1.22 Five
C. 1.25 V
D. 50.0 Five
Solution:

Affiliate 21 Electric Electric current and Direct-Current Circuits Q.127PP
Suppose that during one test a person'south shoes become wet when water spills onto the floor. When this happens, do you expect the reading on the voltmeter to increase, decrease, or stay the same?
Solution:
Given if the shoes get wet the resistance of the person foot article of clothing will exist decreased and the current flow volition be increased. This results increase in the voltmeter reading.

Chapter 21 Electric Current and Direct-Current Circuits Q.128IP
Referring to Example 21-7 Suppose the iii resistors in this circuit have the values R1 = 100.0 Ω, R2 = 200.0 Ω, and R3 = 300.0 Ω, and that the emf of the battery is 12.0 Five. (The resistor numbers are given in the Interactive Figure.)
(a) Find the potential difference across each resistor,
(b) Find the current that flows through each resistor.
Solution:

Affiliate 21 Electric current and Direct-Current Circuits Q.129IP
Referring to Example 21-7 Suppose R1 = R2 = 225 Ω and R3 = R. The emf of the battery is 12.0 V. (The resistor numbers are given in the Interactive Effigy.)
(a) Find the value of R such that the current supplied past the battery is 0.0750 A. (b) Find the value of R that gives a potential difference of 2.65 Five across resistor 2.
Solution:

Chapter 21 Electrical Current and Direct-Current Circuits Q.130IP
IP Referring to Case 21-ix Suppose the resistance of the 126-Ω resistor is reduced past a gene of 2. The other resistor is 275 Ω, the capacitor is 182 μF, and the battery has an emf of 3.00 V.
(a) Does the filial value of the accuse on the capacitor increment, decrease, or stay the same? Explain,
(b) Does the time for the capacitor to charge to lxxx.0% of its final value increment, decrease, or stay the same? Explicate, (c) Find the fourth dimension referred to in function (b).
Solution:

Chapter 21 Electric Current and Straight-Electric current Circuits Q.131IP
IP Referring to Example 21-9 Suppose the capacitance of the 182-μF capacitor is reduced by a cistron of two. The two resistors are 126 Ω and 275 Ω, and the battery has an emf of 3.00 Five.
(a) Find the final value of the charge on the capacitor,
(b) Does the fourth dimension for the capacitor to charge to 80.0% of its last value increment, decrease, or stay the same? Explicate,
(c) Discover the time referred to in part (b).
Solution:

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