# I need some explanation on this

## Homework Statement

[PLAIN]http://img23.imageshack.us/img23/949/unledto.png [Broken]

Go to problem b)

[PLAIN]http://img850.imageshack.us/img850/5388/unledzb.png [Broken]

## The Attempt at a Solution

Now my question is why L + 2x? L is the height and x is the width, why are they adding them? I know $$\lambda$$ is the resistance per unit length, but I don't understand they are adding them. It would make sense if they added the entire arclength (perimeter) of the rectangle

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cepheid
Staff Emeritus
Gold Member
The problem says the rod has negligible resistance, which means that you only need to add up the lengths of the three sides of the rectangle that are formed by nichrome wire. This is one height (L) and two widths (2x).

The problem says the rod has negligible resistance, which means that you only need to add up the lengths of the three sides of the rectangle that are formed by nichrome wire. This is one height (L) and two widths (2x).

OnlyMe
Gold Member
The distance between P & Q is L.

SammyS
Staff Emeritus
Homework Helper
Gold Member
OK!

Resistance is: R = λ(2x + L) + 0(L), because, as cepheid pointed out, the rod has negligible resistance.

cepheid
Staff Emeritus
Gold Member
Code:
  P--------------------
|            x
|
|
| L
|
|
|            x
Q--------------------
Just to be clear, these are the three sides of the rectangle I was referring to. (The fourth side, made by the rod, is not shown). Adding their lengths up, we get:

L + x + x = L + 2x

OK!

Resistance is: R = λ(2x + L) + 0(L), because, as cepheid pointed out, the rod has negligible resistance.
It's okay, OnlyMe explained it to me pretty well lol.

Also, the rod isn't length L, look closely...

cepheid
Staff Emeritus