April 20, 2024
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View All : Main > Topics > DC Circuits > Circuit Variables > SI Units > Problem #1
Problem ID: 246
Problem Filename: cktvars_units_ex1
Keywords:
Circut Description:
  • light
  • LED
Math Method:
  • algebra

Circuit Variables

SI Units

Problem #1

A "night light" illuminates dark hallways and children's rooms at night. Older night lights use incandescent bulbs (tungsten filament in an evacuated glass envelope), while newer night lights use light-emitting diodes (LEDs). The older style night light bulb requires 4 W of power to operate, while a newer LED night light might require about 0.2 W of power. According to the U.S. Department of Energy, a kilowatt-hour costs 9.85 cents for the residential customers, on average (http://www.eia.doe.gov/cneaf/electricity/epm/table5_6_b.html).

During the course of a year, what is the total cost saved by using an LED-based night light instead of the older style night light?