Circuitry-in-the-home-f + LTX v file://cusers TEMP Downloads Circuitry-in the ho
ID: 1634647 • Letter: C
Question
Circuitry-in-the-home-f + LTX v file://cusers TEMP Downloads Circuitry-in the home-etc.pdf file:///C:/Users/TEMP/Downloads/Circuitry-in-the-home-etc.pdf phys 222.01 Su17 NSC clectrical circuitrn in the homeplaee worth up to 10 (ten) bonus points toward one exam 1. Cireuit breakers and fuses are devices that fail when current of a specific threshold or more flows through it. Thcy serve to protect devices on the cireuit from damage and to prevent fires due to overheated wires. Typically the threshold currents are chosen so that if there is no resistance except the wire then the breaker fuse will fail On a 120-V cire in a home, copper wire that is 12-gauge (2.053 mn diameter) is commonly used with 20-A circuit breakers. a. How much power is being dissipated by the wires by 20 A through a 120-V circuit? Almost all of this power becomes thermal energy in the wires! How much resistance does the wire provide if 120 V generates 19.9 A through the wire? What length of 12-gauge copper wire would provide the resistance you calculated in part b.? You may need to look up properties of 12-gauge copper wire If you wanted to ensure that your 20-A breaker is tripped when the wire completes the circuit, would you make the length of wire longer or shorter than the length you calculated in part c.? How many electrons' movement through the wire is measured as 20 A? b. c. d. e. 3:53 PM Type here to search 7/29/2017 2Explanation / Answer
(A) Power = V I
P = 120 x 20
P = 2400 W
(B) V = I R
R = 120 / 19.9 = 6.03 ohm
(C)
resistivity of copper, rho = 1.72 x 10^-8 ohm m
R = rho L / A
6.03 = (1.72 x 10^-8) ( L ) / (pi x (2.053 x 10^-3 / 2)^2)
L = 1160.6 m
(d) to decrease the current, we have to increase the resistance.
so length will be longer.
(e) I = q / t
q = 20 C / s
q = n e
20 = 1.602 x 10^-19 n
n = 1.25 x 10^20 electrons / s