# Homework Help: Power transmission cable

1. Feb 24, 2015

### Matt512

1. The problem statement, all variables and given/known data

A power station supplies a factory with 1MW of electrical power at a p.d of 10KV. The total resistance of both cables between power station and factory is 0.5 ohm. Find the percentage of the power station output power which is delivered to the output factory.How does this figure change if the supply p.d s only 250V.
2. Relevant equations

3. The attempt at a solution
Well , i tried to find I , which is I = p/v = (106)/(103)=1000A
Then i use = I2R
And get 5*105
But i dont know if am on the right way.

2. Feb 24, 2015

### Orodruin

Staff Emeritus
So, what do you think the power you now computed represents?

Also, remember to put units on your numbers.

3. Feb 24, 2015

### Matt512

Well to be honest , i don`t have a clue on how to do this question .But am trying to understand and do it.

4. Feb 24, 2015

### Orodruin

Staff Emeritus
So let us take things one step at a time to figure out what you have computed. In your first step, you say I = P/V. Which values did you put in here and what current does the result represent?

5. Feb 24, 2015

### Matt512

Power= 10MW
P.D =10KV

I = p/v = (106)/(103)=1000A

Well the answer represents the current at the factory ?

6. Feb 24, 2015

### Orodruin

Staff Emeritus
Yes, it is the current at the factory. How does this relate to the current through the cables to and from the factory?

7. Feb 24, 2015

### Matt512

Well i can calculate the power loss by using p=I2R right or p=V2/R

8. Feb 24, 2015

### Orodruin

Staff Emeritus
Yes. So the current through the cables must be the same as through the factory.

You do not have the voltage across the cables, so you must use the first expression. So what you computed is the power loss. How large a portion of the power from the power station does this represent?