Silicon, Circuits, and the Digital Revolution

Worksheet to accompany Lights Out!

1. Use the following graph to fill in this table:

voltage applied current bulb resistance   (V) (A) (ohm) "3 V" bulb:   0.20       0.30       0.40   "6 V" bulb:   0.20       0.30       0.40

2. Find out why the resistance varies with the current flowing through a light bulb.

3. At its normal operating voltage, which light bulb will be brighter?

4. Internal resistance of a battery is an important consideration in the design of a flashlight. Determine the internal resistance of the "1.5 V" voltage sources used to generate the following graph.

"1.5 V" sources load terminal voltage difference from no load voltage current internal resistance     (V) (V) (A) (ohm) AAA cell: light           heavy         D cell: light           heavy         supply: light           heavy

5. How do your values for the AAA and D cells above compare to the values reported in the SCEN103 battery characteristics page?

6. From the following graph of current vs. time for discharging battery, estimate the energy capacity of the battery under the different loading conditions. The area under each curve is the energy capacity.

Battery Loading Duration Average Current Energy Capacity (ohm) (hr) (mA) (mA-hr) 8.8       6.6       4.4       2.2	Discharge of Duracell AAA cell, model MN2400, dated Mar2004

7. How do the values of energy capacity determined above compare to the stated values in the SCEN103 battery characteristics page and at Duracell: OEM page: alkaline cells? Discuss the trend of energy capacity as the current drawn from the battery increases.

8. You should have enough information in these graphs to make an informed design of the 2 AAA cell/"6 V" bulb flashlight.

Comments, suggestions, or requests to ghw@udel.edu. "http://www.physics.udel.edu/~watson/scen103/colloq2000/problems/flashlight-worksheet.html" Last updated April 6, 2000. © George Watson, Univ. of Delaware, 2000.