An extension cord is used with an electric weed trimmer that has a resistance of 17.9 Ω. The extension cord is made of copper (resistivity 1.72 x 10-8 ohm m) wire that has a cross-sectional area of 1.71 x 10-6 m2. The combined length of the two wires in the extension cord is 86.3 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?

(a)

(b)

Explanation:

Part (a)

The total length of copper cord L=86.3 m

The cross sectional area A=1.71×10⁻⁶m²

The resistivity of copper p=1.72×10⁻⁸Ω

Thus the resistance of extension cord is

Part (b)

The resistance of trimmer Rt=17.9 ohms

When voltage of 120V is applied then the current I is passing through series circuit is

Thus the voltage across the trimmer is:

power out to power in less than 100%

= initial pressure

= final pressure = 2

= initial volume

= final volume = /4

= initial temperature = 20 c = 20 + 273 = 293 k

= final temperature = ?

using the equation