# Homework Help: High Electricity Questions.

1. Apr 12, 2013

### Delpo

Can someone give me explanations for the answers to these questions as the book just gives small simple answers?

1)A volume of 1.2x10^-5 m^3 of conducting paint is poured into a glass cylinder of base area 3.0x10^-4 m^2. It fills the cylinder to a height of 40mm. The resistance between the top and bottom surfaces of the paint is 9.2Ω. Resistivity of the paint is 0.069 Ωm
Suppose the paint had been poured into a cylinder with half the base area. What would the value of the resistance between the top and bottom of the surfaces have been?

2)The power stations providing electricity for the National Grid generate electricity at 25kV. The typical demand on an average winter's day in the north-west of England is 6000MW. The current output form the generators is 240kV. Transformers raise the transmission voltage to 400kV. Assuming 100% efficiency in the transformers, the current is 15kA. Each pair of 400kV supergrid conductors has a resistance of 0.034Ωk/m.
How much power is lost per kilometre heating the conductors?

2. Apr 12, 2013

### Staff: Mentor

It would be easier to find your errors if you included the calculation here.

1) did you take the doubled height into account? Both this and the reduced cross-section increase the resistance by a factor of 2, for a total of 4*9.2Ω=36.8Ω.
2) this has a strange unit for the resistance. Ωk/m? Ω/km?
Assuming the second, did you calculate the voltage drop in 1km? Multiply it with the current and you get the same result as the book.