Discussion Questions
8. Explain how a flashlight bulb works. Draw a picture showing the relationship between a bulb's filament and its two terminals. Why does the brightness depend on the current through the bulb? What effect would increasing the voltage across a bulb have on its brightness? Incidentally, light bulbs are not ohmic.
13. Compare the brightness of each identical bulb in Fig. Q13. Explain.
15. If all the resistors in Fig. Q15 are identical, rate them in order of the amount of current passing through each one. Explain.
Problems
1. What is the current in the circuit of Fig. P1 before and after the wire is clipped on at C and B? What happens to the 12-ohm bulb after the wire is attached? The battery has a negligible internal resistance.
3. Each lamp in Fig. P3 has a resistance of 20-ohms. How much current is drawn from the battery before and after the switch is closed? How does the power supplied to the circuit change when the switch is closed? The battery has negligible resistance.
7. A portable generator in a field hospital produces dc at 100 Volts. Five 100-W lmaps are attached in parallel and the string placed across the terminals of the generator. How much current must the source produce for the lamps to operate as designed?
11. What is the equivalent resistance of the circuit in Fig. P11 between terminals A and B? Note that the wires cross but do not make contact at the center.
14,15,16. Determine the equivalent resistance of the circuit shown in P14 between the points:
20. Given that the ammeter in Fig. P20 reads 1 Amp, what is the emf of the ideal dc source as indicated by the voltmeter?
23. A 20-Volt lamp is designed to dissipate 80 W is placed in series with a resistor R and a 60-Volt dc source. What value should R be for the lamp to operate properly?
31. Determine the equivalent resistance of the circuit between points A and B in Fig P31.
37. Given the circuit in Fig. P37, calculate the current in each resistor. What power is delivered by the battery? What is the potential difference between A and C?
38. The battery in Fig. P38 has an emf of 9.0 Volts and an internal resistance of 0.50 ohms. a) What current does it supply? b) What is the total power disspiated by the entire circuit? c) What is the terminal voltage of the battery?
49. Use Kirchhoff's Loop Rule to solve for the currents in branches A-D-C and A-B-C of the circuit in Fig. P49. Then use the Node Rule to find the current in branch A-C.
50. Find the current through each element of the circuit in P50.
51. Apply Kirchhoff's Laws to the circuit of Fig. P51 and solve for the three branch currents. Next simplify the circuit, determine all currents, and check your answers.
52. Solve for the unknown source voltage and the power delivered by the 12-Volt battery in Fig. P52.
Comment--More Network problems next week.