College Physics

Physics & Astronomy

Quiz 4 :

Direct-Current Circuits

Quiz 4 :

Direct-Current Circuits

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Is the direction of current in a battery always from the negative terminal to the positive one Explain.
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No, it depends on the emf of the battery. If the battery has a more emf, than the source emf then the battery acts as a source to the circuit. In such situation, the current will flows from the negative terminal to the positive terminal of the battery. If the battery has less emf than the source emf, then the current will flows from the positive terminal of the battery to the negative terminal of the battery.

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A battery having an emf of 9.00 V delivers 117 mA when connected to a 72.0- load. Determine the internal resistance of the battery.
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The relation between the current I and the emf of the battery img in presence of internal resistance r of the battery is shown below. img Here, R is the load resistance and r is the internal resistance.
Re-arrange the equation to solve for r. img Substitute 9.00 V for img , 0.117 mA for I , and img . img Therefore, the internal resistance r of the battery is img .

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Given three lightbulbs and a battery, sketch as many different circuits as you can.
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Three light bulbs are in series connection with a battery supply of V is as shown in figure 1. img Figure 1
Three Light bulbs are in parallel connection with a battery supply of V is as shown in figure 2. img Figure 2
Two Light bulbs are in series connection and the resultant brightness of these two in parallel with third light bulb with a battery supply V is as shown in figure 3. img Figure 3
Two Light bulbs are in parallel connection and the resultant brightness of these two in series with third light bulb with a battery supply V is as shown in figure 4. img Figure 4
Therefore, the possible connections obtained for three bulbs and a battery are 4.

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Three 9.0- resistors are connected in series with a 12-V battery. Find (a) the equivalent resistance of the circuit and (b) the current in each resistor. (c) Repeat for the case in which all three resistors are connected in parallel across the battery.
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Suppose the energy transferred to a dead battery during charging is W. The recharged battery is then used until fully discharged again. Is the total energy transferred out of the battery during use also W
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A lightbulb marked "75 W [at] 120 V" is screwed into a socket at one end of a long extension cord in which each of the two conductors has a resistance of 0.800 V. The other end of the extension cord is plugged into a 120-V outlet. (a) Draw a circuit diagram, and (b) find the actual power of the bulb in the circuit described.
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A short circuit is a circuit containing a path of very low resistance in parallel with some other part of the circuit. Discuss the effect of a short circuit on the portion of the circuit it parallels. Use a lamp with a frayed line cord as an example.
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(a) Find the current in an 8.00- resistor connected to a battery that has an internal resistance of 0.15 if the voltage across the battery (the terminal voltage) is 9.00 V. (b) What is the emf of the battery
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Connecting batteries in series increases the emf applied to a circuit. What advantage might there be to connecting them in parallel
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(a) Find the equivalent resistance between points a and b in Figure P18.5. (b) Calculate the current in each resistor if a potential difference of 34.0 V is applied between points a and b.
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If electrical power is transmitted over long distances, the resistance of the wires becomes significant. Why Which mode of transmission would result in less energy loss, high current and low voltage or low current and high voltage Discuss.
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Consider the combination of resistors shown in Figure P18.6. (a) Find the equivalent resistance between point a and b. (b) If a voltage of 35.0 V is applied between points a and b , find the current in each resistor.
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If you have your headlights on while you start your car, why do they dim while the car is starting
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Two resistors connected in series have an equivalent resistance of 690 . When they are connected in parallel, their equivalent resistance is 150 . Find the resistance of each resistor.
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Two sets of Christmas lights are available. For set A, when one bulb is removed, the remaining bulbs remain illuminated. For set B, when one bulb is removed, the remaining bulbs do not operate. Explain the difference in wiring for the two sets.
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Consider the circuit shown in Figure P18.8. (a) Calculate the equivalent resistance of the 10.0- and 5.00- resistors connected in parallel. (b) Using the result of part (a), calculate the combined resistance of the 10.0- , 5.00- , and 4.00- resistors. (c) Calculate the equivalent resistance of the combined resistance found in part (b) and the parallel 3.00- resistor. (d) Combine the equivalent resistance found in part (c) with the 2.00- resistor. (e) Calculate the total current in the circuit. (f) What is the voltage drop across the 2.00- resistor (g) Subtracting the result of part (f) from the battery voltage, find the voltage across the 3.00-V resistor. (h) Calculate the current in the 3.00-V resistor.
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Why is it possible for a bird to sit on a high-voltage wire without being electrocuted (See Fig. CQ18.9.)
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Consider the circuit shown in Figure P18.9. Find (a) the potential difference between points a and b and (b) the current in the 20.0- resistor.
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(a) Two resistors are connected in series across a battery. Is the power delivered to each resistor (i) the same or (ii) not necessarily the same (b) Two resistors are connected in parallel across a battery. Is the power delivered to each resistor (i) the same or (ii) not necessarily the same
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Four resistors are connected to a battery as shown in Figure P18.10. (a) Determine the potential difference across each resistor in terms of . (b) Determine the current in each resistor in terms of I.
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