Calculating combined resistance of wires

[toforfiltum]

Homework Statement

Homework Equations

• R ∝ 1/A

The Attempt at a Solution

Since there are six copper wires and a steel core, I added the resistance of all the wires and the core and divided them by 7, though I don't think my approach is right since the resistance of the copper and steel wires are different. As such my answer is about 22.9Ω, which is wrong. The answer is B, 1.6Ω, which is just the quotient of the the total resistance of the six copper wires. Why is the resistance of steel core not taken into account in this case?

 

[haruspex]

Do you know how to calculate the net resistance of resistors in parallel?

 

[toforfiltum]

Ermm...yes. But why is the steel not taken into account?

 

[haruspex]

Ermm...yes. But why is the steel not taken into account?

Why are you so sure it isn't? Have you done the calculation taking the steel into account?

 

[toforfiltum]

Oh, so is the working 6(_1/10) + _1/100 correct for 1/R?

 

[haruspex]

Oh, so is the working 6(_1/10) + _1/100 correct for 1/R?

Yes.

 

[toforfiltum]

Thanks. So is this combined resistance of six different copper wires and steel less than a power cable just made up of one copper wire of the same cross-sectional area?

 

[haruspex]

Thanks. So is this combined resistance of six different copper wires and steel less than a power cable just made up of one copper wire of the same cross-sectional area?

What do you think?

 

[toforfiltum]

I think the resistance of six different copper wires and the steel would be lesser. However if it's just the six copper wires without the steel, then they would be the same.

 

[haruspex]

I think the resistance of six different copper wires and the steel would be lesser. However if it's just the six copper wires without the steel, then they would be the same.

Quite so.

 

[toforfiltum]

Why quite so? Is it not really correct?

 

[haruspex]

Why quite so? Is it not really correct?

"Quite so" means, yes, that is exactly correct. (British English idiom?)

 

[toforfiltum]

Oh I see.

 

[Neelima]

Since resistance values are given we need think about type of wire.
From situation they are in parallel connection.
Please see the attachment

 

[haruspex]

Since resistance values are given we need think about type of wire.
From situation they are in parallel connection.
Please see the attachment

Yes, the OP got this in post #5. Five years ago.