Discussion Questions
2. Figure Q2 shows several 9 Volt batteries opened up so we can look inside. Explain what you see.
4. What happens when you turn the key in the ignition of your automobile? Should you start your car on a cold rainy night with the wipers, lights, heater, and defroster all on? Explain.
6. Suppose you parked your car and left the lights on all night. Why would you have trouble starting it the next day? Would it be more bothersome to start on a really cold winter's day? After several tries, the engine just makes some disheartening clicking noises and you've had it--what has happened? A friend comes to your aid and "jump starts" your car. How is that done and what does it accomplish?
8. Figure Q8 shows an ordinary metal-body flashlight. Explain how it works and discuss the significance of the arrangement of the dry cells.
16. High-voltage cables are generally uninsulated, and a bird standing on one of them may have its feathers puffed up. Why? Why aren't our little feathered friends electrocuted on their perches? Could a chicken walk safely on the third rail of an electrified railroad?
Problems
1. The moving nonconducting belt of a van de Graaff generator carries 10 micro C of charge up to the metal sphere each second. Determine the corresponding current.
5. The starter motor in an automobile is a small but powerful electrical device that "turns over" the main gasoline engine, moving it through a cycle to get it started. Typically, it will draw about 180 A from the battery for perhaps 2 seconds. How much charge flows through the circuit?
13. A battery is rated at 10 amp-hours. How much charge does that correspond to?
19. We widh to make up a panel of silicon solar cells that will provide at least 440 mA at 9 Volts when placed in an appropriately illuminated region. Given that each cell provides 22 mA at 0.45 Volts, design the panel.
24. A small high-torque variable-speed dc motor requires an input of 10 mA at 3 Volts. Determine the electrical resistance of the motor.
32. A nichrome wire with a cross-sectional area of 1.5 x 10**(-6) m is to be used in a heater. If the design calls for a 3 ohm coil, what length of wire will be needed?
37. A narrow rod of pure iron has a a resistance of 0.10 ohms at 20 C. (a) What is its resistance at 50 C? (b) A narrow rod of manganin has a resistance of 0.10 ohms at 20 C. What is its resistance at 50 C?
39. A portable tape recorder has a plate on its underside indicating that it uses 1 W at 9 Volts dc. What net current does it draw from the dc battery?
40. Referring to question 39, what is the net resistance of the tape recorder?
55. A powerhouse near a waterfall has a large dc generator that produces electricity for a factory 0.50 miles away. The energy is transmitted over two cable each with a resistance of 0.25 ohms/mile. Given that the factory requires 45 kW at a voltage of 110 Volts to run its equipment, what must be the output of the powerhouse?
61. The moving nonconducting belt of a van de Graaff generator carries 10 micro C of charge up to the metal sphere each second. The steady-state potential difference the sphere and the source is 3 million Volts. What minimum power must be supplied to the generator to sustain its operation?