Lightbulb A is marked \"10.0 W 120 V,\" and lightbulb B is marked \"25.0 W 120 V

Question

Lightbulb A is marked "10.0 W 120 V," and lightbulb B is marked "25.0 W 120 V." These labels mean that each lightbulb has its respective power delivered to it when it is connected to a constant 120-V source. (a) Find the resistance of each lightbulb. R(10.0 W 120 V) = ? R(25.0 W 120 V) = ? B) During what time interval do 1.40 C pass into lightbulb A? C) In what time interval do 2.00 J pass into lightbulb A? D) what mechanisms allows the energy to leave and exit? E) Find the cost of running lightbulb A continuously for 30.0 days, assuming the electric company sells its product at $0.110 per kWh?

Explanation / Answer

for each bulb, resistance = V^2 / Power so

first bulb

R = 120^2 / 10 = 1440 ohms

second bulb

    R = 120^2 / 25 = 576 ohms

B) current in first bulb = 120 / 1440 = 0.08333

time = 1.40 / 0.08333 = 16.8 seconds

C) time = energy/power = 2.0 / 25 = 0.08 seconds

D) radiation

E) bulb A... 10 Watts * 24 hr * 30 days = 7200 Watt-hr = 7.20 kW-hr

7.20 * $0.110 = $0.792 is the cost

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