Question

Light bulb A is marked "25 W 120 V" and light bulb B "100 W 120 V"; this means that each bulb converts its respective power when plugged into a constant 120 V source, Find the resistance of each bulb, How long does it take for 1.00 C to pass into bulb A? Is this charge different in any way upon its exit from the bulb versus it entry? Explain, How long does it take for 1.00 J to pass into bulb A? By what mechanism does this energy enter and exit the bulb? Explain, Find the cost of running the light bulb A continuously for 30.0 days if the electric company sells its product at $0,110 per kWh.

Answer 1

Power = V^2 /R

R = V^2/power

Ra = 120*120/25 = 576 ohm

Rb = 120*120/100 = 144 ohm

b) Current in bulb A is ; I = V/R = 120/576 = 0.21 A

Hence it will take 1/0.20833 sec = 4.8 sec

c) It decreases while coming out as the electrons lose energy as heat while travelling throught the filament to produce heat and light.

d) We know that the power of bulb A is 25W, hence it will take 1/25 sec = 40 milisec