Light bulb problem (Power, Reistance Voltage...etc..)

Question

A 3-way light bulb has 3 brightness settings (low, medium, & high), but only 2 filaments.

a.) a particular 3-way lightbulb connected across a 120-V line can dissipate 60W, 120W, or 180 W. Describe how the two filaments are arranged in the bulb, and calculate the resistance of each filament.

b.) suppose the filament w/ the higher resistance burns out. How much power will the light bulb dissipate on each of the 3 brightness settings? What will be the brightness (l,m,h) on each setting?

c.) Repeat part b for the situation where it is the filament w/ the lover resistance that burns out.

thank you!

Answer 1

a) The two filaments are 60 and 120 watts, with both on (in parallel) you get 180 watts.

P = E²/R

60 = 120²/R

R = 240 ohms

120 = 120²/R

R = 120 ohms

b) 60 watt filament burns out, you will get 0, 120, 120 watts of light

c) 120 watt filament burns out, you will get 60, 0, 60 watts of light

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