An extension cord is used with an electric weed trimmer that has a resistance of

Question

An extension cord is used with an electric weed trimmer that has a resistance of 15.4 . The extension cord is made of copper wire that has a cross-sectional area of 1.23 x 10-6 m2. The combined length of the two wires in the extension cord is 86.4 m. (a) Determine the resistance of the extension cord. (b) The extension cord is plugged into a 120-V socket. What voltage is applied to the trimmer itself?

An electric furnace runs 7.9 hours a day to heat a house during January (31 days). The heating element has a resistance of 7.2 and carries a current of 16.7 A. The cost of electricity is $0.10/kWh. Find the cost of running the furnace during January.

Explanation / Answer

Extension cord is connected in series with electric weed timmer
a) ? of extension cord = 1.71 x 10-8 Om, l =86.4 m, a= 1.23 x 10-6 m2
R of extension cord =l/a = (1.71 x 10-8 * 86.4)/1.23 x 10-6 = 

 

Equivalent resistance of circuit= 15.4 + (1.71 x 10-8 * 86.4)/1.23 x 10-6 = 1.201+15.4=16.6011

 

 

b) current flowing through circuit = 120/14.9198= 8.043 A approx
Voltage across trimmer = 13.7 x 8.043 = 110.189 V approx

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