Question

a.What is the current in 50w thee filament of light bulb when you turn the light on? Electric socket supply electricity at about 110V.

b. how much charge does flow through the filament during 20.0 seconds?

c. how many electrons pass during this time?

d. what is the resistance of the filament?

e. what is your monthly payment if you keep the light bulb on for 4 hours every day?

Answer 1

4A

Power is given by

P = V*i

i = P/V

i = 50 W/110 V = 0.4545 Amp

4B.

i = dq/dt

dq = charge = i*dt

dq = 0.4545*20 = 9.09 C

4C.

dq = n*e

n = number of electrons = dq/e

n = 9.09/(1.6*10^-19) = 5.68*10^19 electrons

4D.

Ohm's law

V = i*R

R = V/i

R = 110/0.4545

R = 242 ohm

4E.

Power of bulb = 55 W

time per month = 30*4 = 120 hr

energy = Power*time

E = 55*120 = 6600 W-hr

1 kWh = 1000 W-hr

6600 W-hr = 6.6 kWh

Price of 1 kWh = 55 cents

Price of 6.6 kWh = 55*6.6 = 363 cents = $3.63

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