2) A three-way light bulb has three brightness settings (low, medium, high) but

Question

2) A three-way light bulb has three brightness settings (low, medium, high) but only two filaments. (a) A particular three-way light bulb connected across a 120 V line can dissipate 60 W, 120 W, or 180 W. Describe how the two filaments are arranged i the bulb, and calculate the resistance of each filament. (b) Suppose the filament with the higher resistance burns out. How much power will the bulb dissipate on each of the three brightness settings? What will be the brightness (low, medium, high) on each setting? Repeat part (b) for the situation in which the filament with the lower resistance burns out.

Explanation / Answer

Answer:

The two filaments will be 60 and 120 Watts and both in parallel give 180 watts

For 60 Watt

P = V2/R

60 = 120 x 120 / R

R = 240 ohms

For 120 Watt

120 = 120 x 120 / R

R = 120 ohms

B) 60 watt filament (high resistance) burns out, you will get 0, 120, 120 watts of light

C) 120 watt filament (Low resistance) burns out, you will get 60, 0, 60 watts of light

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