Electricity Preview Understanding Concepts Reading Skills Interpreting Graphics

Understanding Concepts 1. Over a period of 5 min, 7,500 C is found to have traveled past a particular point in a circuit. How much current must have been flowing through the circuit? A. 25 A B. 1,500 V C. 7,500 V D. 37,500 A

Understanding Concepts, continued 1. Over a period of 5 min, 7,500 C is found to have traveled past a particular point in a circuit. How much current must have been flowing through the circuit? A. 25 A B. 1,500 V C. 7,500 V D. 37,500 A

Understanding Concepts, continued 2. If 0.5 A is flowing through a household light bulb and the bulb is plugged into a 120 V outlet, what is the bulb’s power output? F. 0.5 Ω G. 60 W H. 120 Ω I. 240 W

Understanding Concepts, continued 2. If 0.5 A is flowing through a household light bulb and the bulb is plugged into a 120 V outlet, what is the bulb’s power output? F. 0.5 Ω G. 60 W H. 120 Ω I. 240 W

Understanding Concepts, continued 3. To cool a microprocessor, an engineer designs a circuit with a battery and four tiny fans. If the voltage across each fan must be identical, how should the circuit be designed? A. The circuit should resemble a circle made of a single wire, with the battery and two fans in a series. B. There should be at least one fuse or circuit breaker for each fan. C. The fans should be connected in parallel in the circuit. D. Each fan must offer the same amount of resistance.

Understanding Concepts, continued 3. To cool a microprocessor, an engineer designs a circuit with a battery and four tiny fans. If the voltage across each fan must be identical, how should the circuit be designed? A. The circuit should resemble a circle made of a single wire, with the battery and two fans in a series. B. There should be at least one fuse or circuit breaker for each fan. C. The fans should be connected in parallel in the circuit. D. Each fan must offer the same amount of resistance.

Understanding Concepts, continued 4. Before the adoption of SI units, the power output of some engines was measured in horsepower. One horsepower is equal to approximately 746 W. If a 5.0 horsepower engine is putting out 17 A of current, what is the voltage of the circuit?

Understanding Concepts, continued 4. Before the adoption of SI units, the power output of some engines was measured in horsepower. One horsepower is equal to approximately 746 W. If a 5.0 horsepower engine is putting out 17 A of current, what is the voltage of the circuit? Answer: 220 volts

Understanding Concepts, continued 5. Why are circuit breakers preferable to fuses?

Understanding Concepts, continued 5. Why are circuit breakers preferable to fuses? Answer: They don't have to be replaced.

Understanding Concepts, continued 6. Why aren’t resistors made from copper?

Understanding Concepts, continued 6. Why aren’t resistors made from copper? Answer: Copper conducts too well.

TURNING LIGHT INTO ELECTRICITY Reading Skills TURNING LIGHT INTO ELECTRICITY On a clear day, sunlight strikes Earth’s surface with an intensity of approximately 1,000 W/m2. If all of that energy could be collected and transformed into electricity, there would be more than enough to run all the homes and businesses on the planet. At this point, the most efficient solar cells in existence capture only about 15% of the energy of sunlight, or approximately 150 W/m2.

Reading Skills, continued TURNING LIGHT INTO ELECTRICITY, continued Solar cells can be constructed in a variety of shapes and sizes. Individual cells, regardless of their size, always produce a voltage of about 0.5 V. However, larger cells produce more current, and therefore more power (measured in W), because power is current times voltage. When multiple solar cells are connected in series, their voltages are added, but the current remains the same. When solar cells are connected in parallel, their current is added, but the voltage remains the same. Solar panels consist of a grid of cells, some connected in series and some in parallel, so that both voltage and current can be raised to useful levels.

Reading Skills, continued 7. A particular solar panel has a potential difference of 48 V. What is the minimum number of solar cells the panel could have? A. 12 B. 24 C. 48 D. 96

Reading Skills, continued 7. A particular solar panel has a potential difference of 48 V. What is the minimum number of solar cells the panel could have? A. 12 B. 24 C. 48 D. 96

Reading Skills, continued 8. A solar panel measuring 15 m by 10 m is operating at the maximum efficiency currently possible. If the panel has a potential difference of 225 V, how much current is the panel producing? F. 100 W G. 100 A H. 150 W I. 150 A

Reading Skills, continued 8. A solar panel measuring 15 m by 10 m is operating at the maximum efficiency currently possible. If the panel has a potential difference of 225 V, how much current is the panel producing? F. 100 W G. 100 A H. 150 W I. 150 A

Interpreting Graphics The schematic diagram below depicts an electrical circuit. Use this schematic to answer questions 9–11. 9. Which bulb burning out would mean that no current could flow through the circuit? A. bulb A B. bulb B C. bulb C D. bulb D

Interpreting Graphics, continued 9. Which bulb burning out would mean that no current could flow through the circuit? A. bulb A B. bulb B C. bulb C D. bulb D

Interpreting Graphics, continued 10. Which bulbs are connected in parallel with each other? F. Bulb A is connected in parallel with bulb C. G. Bulb B is connected in parallel with bulb D. H. Bulb A is connected in parallel with bulbs B and D. I. Bulb C is connected in parallel with bulbs B and D.

Interpreting Graphics, continued 10. Which bulbs are connected in parallel with each other? F. Bulb A is connected in parallel with bulb C. G. Bulb B is connected in parallel with bulb D. H. Bulb A is connected in parallel with bulbs B and D. I. Bulb C is connected in parallel with bulbs B and D.

Interpreting Graphics, continued 11. What must change in the circuit for the bulbs to light?

Interpreting Graphics, continued 11. What must change in the circuit for the bulbs to light? Answer: The switch must be closed.

Interpreting Graphics The following graphic displays the resistance graphs of two thermistors. Use this graphic to answer questions 12–13. 12. At approximately what temperature do the two thermistors experience the same resistance? A. 0 °C B. 50 °C C. 100 °C D. The two thermistors never experience the same resistance.

Interpreting Graphics The following graphic displays the resistance graphs of two thermistors. Use this graphic to answer questions 12–13. 12. At approximately what temperature do the two thermistors experience the same resistance? A. 0 °C B. 50 °C C. 100 °C D. The two thermistors never experience the same resistance.

Interpreting Graphics 13. Which of the two thermistors is more likely to be made of platinum wire? Which is more likely to be made of manganese oxide?

Interpreting Graphics 13. Which of the two thermistors is more likely to be made of platinum wire? Which is more likely to be made of manganese oxide? Answer: B, platinum; A, manganese oxide