What is the resistance of a wire if its diameter is doubled?

  • Thread starter Kevin J
  • Start date
57
2
This was a MCQ question on one of my Cambridge IGCSE Exams, the answer key said that the resistance would decrease by 16 folds (1/16 less then the previous one), I don't know how they got 16 from? (Apparently, I answered 1/4 and it was wrong)
 
7,702
4,376
Your question doesn't sound like homework. But why did you say 4? Are you thinking DC or AC?
 
188
69
If DC resistance is directly proportional to crossectional area, then 1/4 sounds right.
πR∧2 VERS. π(2R)∧2 (Assuming the length is constant.)
 
Last edited:
57
2
Here's the question, the mark scheme says it's D, how do you get D?
20181109_215224.jpeg
 

Attachments

ChemAir

Gold Member
127
117
It says the new cylinder is the same volume as the old one.
 
57
2
19,450
3,892
The volume of a cylinder is $$V=\pi\frac{D^2}{4}L$$If D doubles and V remains constant what does L have to do?
 
27
25
Here's the question, the mark scheme says it's D, how do you get D? View attachment 233716
It doesn't say anything, it was a question from CAMBRIDGE IGCSE
I have a feeling that the length decreases right?
I does in fact mention the length. It states the volume of the putty remains constant as the diameter is increased by twice. For that to be true, the length must also change. Remember that resistance is approximated from resistivity and is inversely proportional to the cross-sectional area of the putty while also being proportional to the putty's length. If the length of the putty decreases while the area increases, the resistance will decrease by the seemingly "too large" factor shown above. Hope this helps.

The easiest way to handle these problems is to substitute in for some numbers and see what happens when you change the parameters.
 
Last edited:

Related Threads for: What is the resistance of a wire if its diameter is doubled?

Replies
4
Views
599
Replies
3
Views
4K
  • Last Post
Replies
7
Views
3K
Replies
3
Views
26K
  • Last Post
Replies
4
Views
1K
Replies
8
Views
2K
Replies
21
Views
6K
Replies
5
Views
3K
Top