Register to reply

Inductance of a coil

by jaejoon89
Tags: coil, inductance
Share this thread:
jaejoon89
#1
Nov20-08, 04:13 AM
P: 195
1. The problem statement, all variables and given/known data

How will a coil's self inductance change if you unwind it and then re-wind half of the length of wire into a coil with the same diameter but with half of the number of turns?

The answer is that it will decrease by 1/4, but I don't understand why it isn't 1/2 instead.

2. Relevant equations


phi (magnetic flux) = LI (where L is inductance, I is current)
n = N/l where "l" is length
B = mew naught * n * I

3. The attempt at a solution

original: L = phi/I = (NBAcostheta) / I = (N* mew naught *n*I*costheta) / I
Now the L with the proposed change: L' = (N/2)* mew naught * ((N/2) / (l/2))* costheta = 1/2 L
Phys.Org News Partner Science news on Phys.org
Flapping baby birds give clues to origin of flight
Prions can trigger 'stuck' wine fermentations, researchers find
Socially-assistive robots help kids with autism learn by providing personalized prompts
Vuldoraq
#2
Nov20-08, 07:26 AM
P: 272
I think it's because you have confused the length of the solenoid, l, with the length of the wire, 2*pi*R*l, where R is the radius of the coil. The length of the solenoid hasn't changed, only the number of turns per unit length (and the wire's length) have dropped.

Edit:Woopsey, no solenoid mentioned, sorry I've been doing a lot of these and went tunnel vision. Your right the length is halved. Where does your N come from in the NBAcostheta/I?


Register to reply

Related Discussions
What is the theoretical limit to coil inductance over coil resistance? Electrical Engineering 15
Self inductance of a solonoidal coil Introductory Physics Homework 1
Inductance of a coil in an AC L-R circuit Introductory Physics Homework 4
Finding the Inductance of a coil Introductory Physics Homework 2