A 160.0 km long electric power line made out of copper is installed during the Spring months at an average temperature of 10.2 °C.
1) What is the change in the length of the power line on a hot summer day, when the temperature is 32.1 °C? The coefficient of linear expansion for copper is 1.62×10^(-5) 1/C°. Use a positive sign for an increase in length and negative for a decrease.
2) What is the change in the length of the cable on a -28.7 °C cold Winter day?

1.+160.0567km

2.-0.102km

Explanation:

Given initial length L1=160Km

L2=?

Initial temperature=10.2°C

Final temperature=32.1°c

Coefficient of linear expansivity a= 1.62*10^-5per Celsius

1: a=L2-L1/L1*∆T

(L2-160/160*21.9)=1.62*10^-5

L2-160=0.0567

L2= 0.0567+160

L2=160.0567Km

2.∆L=? at -28.7°C

Also a=∆L/L1∆T

We're ∆L= aL1∆T

1.65*10^-5*160*(-28.7-10.2)

=-0.102km

r=rho l/a where a is the area, l is the length and rho is resistivity so the greater the area the lesser the resistance thats why the earth pin is thicker bcos current follow the shortest path, so less resistive .