5. Two light bulbs, A and B, are connected across a 12ov voltage source. Light b

Question

5. Two light bulbs, A and B, are connected across a 12ov voltage source. Light bulb A has a power rating of 25W and light bulb B has a power rating of 100W a. Which light bulb has a greater resistance? b. Which light bulb carries more current? 6. How much current is supplied by a 24ov generator delivering 120kW of power? 7. A 240v clothes drier draws 16 A of current for a period of 45 minutes. a. How much energy, in joules, does the drier consume? (HINT: Determine the power rating of the drier first) b. How much energy, in kilowatt-hours, does the drier consume? 8. An electric alarm clock uses a 5.0-W motor and runs all day, every day. year? a. How much energy, in kilowatt-hours, does alarm clock consume in one b. lf electricity costs $0.10 per kilowatt-hour, determine the yearly cost of running the clock.

Explanation / Answer

5.

bulbs A,B are connected across a 120 V battery

A ---25 W,
B --- 100 Wrating then

the power dissipation is P = I^2*R

a) light B has greater resistance

b) bulb A carries more current

6.

   V = 240 v, P = 120000 W

power P = v*I ==> I = P/V = 120000 /240 = 500 A

7.

a)   v = 240 V, I = 16 A
power P = v*I = 240*16 = 3840 W

drier can consume the electrical energy of 3840 J/s = 3.840 kW
b)

kwh = 3.6*10^6 Ws ==> 3.840*3600 kWh = 13824 kWh

8. energy consumed by the alarm clock of 5 W motor runs all day every day

  
in one year it can consume 5*86400*365 W = 157680.000 kW *3600 = 567648000 kWh

b) cost is 567648000*0.10 = 56764800 dollars

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