### SCEN103 Midterm Exam

#### Jan. 26, 1998

For full credit, work must be shown, including formulas used and algebraic and numerical steps. Answers must include units.

1. (2 pts.)
A 1000 W toaster oven is drawing 8.7 A of current as it heats a slice of frozen pizza. When a blender is turned on simultaneously at the same outlet, a 15 A circuit breaker opens the kitchen circuit to avoid overheating of the household wiring. The power rating of the blender must exceed what value?

2. (2 pts.)
Draw a schematic of the circuit that we used to measure the resistance of a cylinder of Play-Doh, indicating the correct placement of power supply, ammeter, and voltmeter.

3. (1 pt.)
What are the chief differences between a AA battery and a D battery?

4. (1 pt.)
Why is alternating current (ac) more widely used than direct current (dc) for distribution of electrical power?

5. (2 pts.)
A 6.0 ohm resistor is connected to an aging 9.0 V battery. The current flow that results is 0.6 A. What must the internal resistance of the battery be?

(2 pts.)
What fraction of the delivered power is lost to the internal resistance?

6. (2 pts.)
 In the circuit at the right, R2 has a larger resistance than R1. Which resistor is hotter (dissipating more power)? Explain your reasoning.

7. (2 pts.)
 Again, R2 has a larger resistance than R1. Which resistor is hotter ? Explain your reasoning.

8. (2 pts.)
 In the circuit at the right, the lamps are identical; i.e., each lamp has the same resistance. Describe the relative brightness of each lamp.

9. (2 pts.)
 Lamp A is subsequently "shorted out" with a wire of negligible resistance as shown. Again, describe as thoroughly as you can the changes in brightness of the two lamps.

10. (2 pts.)
 Describe several fundamental flaws in this picture, intended to represent an atom of lithium (atomic number 3).

"http://www.physics.udel.edu/~watson/scen103/98w/exams/mid98win.html"
Last updated Feb. 6, 1998.
Copyright George Watson, Univ. of Delaware, 1996.