Chapter 27 Flashcards
(20 cards)
To maximize the percentage of the power from the emf of a battery that is delivered to a device external to the battery, what should the internal resistance of the battery be?
(a) It should be as low as possible.
(b) It should be as high as possible.
(c) The percentage does not depend on the internalresistance.
a
With the switch in the circuit of the top figureclosed, there is no current in R2 (in series) because thecurrent has an alternate zero-resistance paththrough the switch. There is current in R1, andthis current is measured with the ammeter (adevice for measuring current) at the bottom ofthe circuit. If the switch is opened (the bottomfigure), there is current in R2. What happensto the reading on the ammeter when theswitch is opened?
(a) The reading goes up.
(b) The reading goes down.
(c) The reading does not change.
b
With the switch in the circuit of the top figureclosed, there is no current in R2 (in parallel) because thecurrent has an alternate zero-resistance paththrough the switch. There is current in R1, andthis current is measured with the ammeter (adevice for measuring current) at the bottom ofthe circuit. If the switch is opened (the bottomfigure), there is current in R2. What happensto the reading on the ammeter when theswitch is opened?
(a) The reading goes up.
(b) The reading goes down.
(c) The reading does not change.
a
In the figure, a third resistor is added in series with thefirst two. What happens to the current in the battery?(a) increases,
(b) decreases,
(c) remains the same.
b
In the figure, a third resistor is added in parallel with thefirst two. What happens to the current in the battery?(a) increases,(b) decreases,(c) remains the same.
a
A homeowner wishes to install low-voltage landscapelighting in his back yard. To save money, he purchasesinexpensive 18-gauge cable, which has a relatively highresistance per unit length. This cable consists of two side-by-side wires separated by insulation, like the cord on anappliance. He runs a 200-foot length of this cable from thepower supply to the farthest point at which he plans toposition a light fixture. He attaches light fixtures across thetwo wires on the cable at 10-foot intervals so that the lightfixtures are in parallel. Because of the cable’s resistance, thebrightness of the lightbulbs in the fixtures is not as desired.Which of the following problems does the homeownerhave?
a) All the lightbulbs glow equally less brightly thanthey would if lower-resistance cable had been used.
(b) The brightness of the lightbulbs decreases as youmove farther from the power supply
b
A circuit breaker is wired:
1. in series with the device it is protecting.
2. in parallel.
3. neither in series or in parallel.
4. It is impossible to tell.
1
A battery has some internal resistance. Can the potentialdifference across the terminals of the battery be equal toits emf?
1. No.
2. Yes, if the battery is absorbing energy by electricaltransmission.
3. Yes, if more than one wire is connected to eachterminal.
4. Yes, if the current in the battery is zero.
5. Yes; no special condition is required.
4
Several resistors are connected in series. Which of thefollowing statements is correct? Choose all that arecorrect.
1. The equivalent resistance is greater than any of theresistances in the group.
2. The equivalent resistance is less than any of theresistances in the group.
3. The equivalent resistance depends on the voltageapplied across the group.
4. The equivalent resistance is equal to the sum of theresistances in the group.
5. None of those statements is correct
1, 4
What is the time constant of the circuit shown in that has 5 resistances in series and 5 capacitors in parallel? Each of the five resistors has resistance R, andeach of the five capacitors has capacitance C. The internal resistance of the battery is negligible.
25RC
When resistors with different resistances are connected in series, which of the following must be the same for each resistor? Choose all correct answers.
1. potential difference
2. current
3. power delivered
4. charge entering
5. none of these answers
2, 4
When resistors with different resistances are connectedin parallel, which of the following must be the same foreach resistor? Choose all correct answers.
1. potential difference
2. current
3. power delivered
4. charge entering
5. none of these answers
1,
The two headlights of a car are wired:
1. in series with each other.
2. in parallel.
3. neither in series or in parallel.
4. It is impossible to tell
2
Several resistors are connected in parallel. Which of thefollowing statements are correct? Choose all that arecorrect.
1. The equivalent resistance is greater than any of theresistances in the group.
2. The equivalent resistance is less than any of the resistancesin the group.
3. The equivalent resistance depends on the voltage appliedacross the group.
4. The equivalent resistance is equal to the sum of theresistances in the group.
5. None of those statements is correct
2,
A series circuit consists of three identical lampsconnected to a battery as shown in the figure. Theswitch S, originally open, is closed. What then happensto the brightness of lamp B?1. It increases.
2. It decreases somewhat.
3. It does not change.
4. It drops to zero.
1
A series circuit consists of three identical lampsconnected to a battery as shown in the figure. Theswitch S, originally open, is closed. What happens to thebrightness of lamp C?1. It increases.
2. It decreases somewhat.
3. It does not change.
4. It drops to zero.
4
A series circuit consists of three identical lampsconnected to a battery as shown in the figure. Theswitch S, originally open, is closed. What happens to thepotential difference across lamp A?
1. It increases.
2. It decreases somewhat.
3. It does not change.
4. It drops to zero.
1 (because there is more current since there is less resistance)
A series circuit consists of three identical lampsconnected to a battery as shown in the figure. Theswitch S, originally open, is closed. What happens tothe potential difference across lamp C?
1. It increases.
2. It decreases somewhat.
3. It does not change.
4. It drops to zero.
4
series circuit consists of three identical lampsconnected to a battery as shown in the figure. Theswitch S, originally open, is closed. What happens to thetotal power delivered to the lamps by the battery?
1. It increases.
2. It decreases somewhat.
3. It does not change.
4. 0
1 (current increases since less resistance)
When operating on a 120-V circuit, an electric heaterreceives 1.30 × 10^3 W of power, a toaster receives1.00 × 10^3 W, and an electric oven receives 1.54 × 10^3W. If all three appliances are connected in parallel ona 120-V circuit and turned on, what is the total currentdrawn from an external source?
1. 24.0 A
2. 32.0 A
3. 40.0 A
4. 48.0 A
5. none of those answers
2
