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# A-level OCR physics resistivity and the national grid watch

1. Hi, I was wondering if someone could help me on a few questions I am unsure on.
1) explain why overhead cables should have a low density.
2)An aluminium cable has a length 15km and consists of a bundle of 10 wires (individual radius 1cm), resistivity of aluminium= 2.65x10^-8 and density of aluminium=2720 kgm3.
Calculate the resistance
If the cost of constructing an aluminium cable is 20 pounds per kg, calculate the cost used in the cable.
2. Sorry you've not had any responses about this. Are you sure you've posted in the right place? Here's a link to our subject forum which should help get you more responses if you post there.

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4. (Original post by Anonsfk)
Hi, I was wondering if someone could help me on a few questions I am unsure on.
1) explain why overhead cables should have a low density.
2)An aluminium cable has a length 15km and consists of a bundle of 10 wires (individual radius 1cm), resistivity of aluminium= 2.65x10^-8 and density of aluminium=2720 kgm3.
Calculate the resistance
If the cost of constructing an aluminium cable is 20 pounds per kg, calculate the cost used in the cable.
Density is directly related to mass. Density is kept low so that the mass of the wire is low else there will be sagging in the cable due to its own weight. In Q.2 ) you have to use the formula Resistance = resistivity x ( length / area ) . Resistivity and length ( convert to meters) are given and area of single wire can be calculated from pi x radius^2 To calculate resistance multiply the area by number of wires ( 10 ). In Q.3 calculate mass by formula density x volume. Hence calculate the cost.
5. (Original post by Anonsfk)
Hi, I was wondering if someone could help me on a few questions I am unsure on.
1) explain why overhead cables should have a low density.
2)An aluminium cable has a length 15km and consists of a bundle of 10 wires (individual radius 1cm), resistivity of aluminium= 2.65x10^-8 and density of aluminium=2720 kgm3.
Calculate the resistance
If the cost of constructing an aluminium cable is 20 pounds per kg, calculate the cost used in the cable.
Low density prevents sagging but more importantly, it means the weight of cables can be kept lower. This results in less stress loading on the pylons, cable supports, ceramic spacers and pylon foundations and in turn, less loading from wind, weight of ice and snow etc.

Combined, the reduced engineering requirements keep the building and running costs down: manufacture requires less material with less stringent physical properties, easier to erect structures, reduction in through-life maintenance of the cable infrastructure

The electricity company that can keep these costs down have a competitive advantage by offering a lower price service to consumers than their rivals.

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