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Finding induced emf of solenoid

by number14
Tags: giancoli, mastering physics, solenoid
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number14
#1
Mar5-09, 10:24 PM
P: 7
1. The problem statement, all variables and given/known data
A 800-turn solenoid, 18 cm long, has a diameter of 2.9 cm. A 15-turn coil is wound tightly around the center of the solenoid.
If the current in the solenoid increases uniformly from 0 to 3.1 A in 0.28 s, what will be the induced emf in the short coil during this time?


2. Relevant equations

Emf=delta_flux/delta_t

3. The attempt at a solution
I keep getting the wrong answer. Originally I just plugged in 800 and 15 for the n's, but then I used turns per meter. Both were wrong. I think I may be using the wrong equation. Any help would be appreciated!
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alphysicist
#2
Mar5-09, 11:36 PM
HW Helper
P: 2,249
Hi number14,

Quote Quote by number14 View Post
1. The problem statement, all variables and given/known data
A 800-turn solenoid, 18 cm long, has a diameter of 2.9 cm. A 15-turn coil is wound tightly around the center of the solenoid.
If the current in the solenoid increases uniformly from 0 to 3.1 A in 0.28 s, what will be the induced emf in the short coil during this time?


2. Relevant equations

Emf=delta_flux/delta_t

3. The attempt at a solution
I keep getting the wrong answer. Originally I just plugged in 800 and 15 for the n's, but then I used turns per meter. Both were wrong. I think I may be using the wrong equation. Any help would be appreciated!
What did you do to get your answers? (what equations did you use, and what numbers did you plug into them)
number14
#3
Mar6-09, 12:19 AM
P: 7
I used B=(mu_0 *N*I)/l delta_flux = B*pi*r^2 and
Emf=-N * delta_flux/delta_t

N=15, I=3.1, l=.18, delta_t=.28 , r=.0145

and I got: 3.6 * 10^-5

alphysicist
#4
Mar6-09, 12:33 AM
HW Helper
P: 2,249
Finding induced emf of solenoid

Quote Quote by number14 View Post
I used B=(mu_0 *N*I)/l delta_flux = B*pi*r^2 and
Emf=-N * delta_flux/delta_t

N=15, I=3.1, l=.18, delta_t=.28 , r=.0145

and I got: 3.6 * 10^-5
I'm not getting that answer from using those numbers. What are you getting for just the B part by itself?
number14
#5
Mar6-09, 01:20 AM
P: 7
B=3.3*10^-4
number14
#6
Mar6-09, 01:23 AM
P: 7
Wait, this time i got 1.2*10^-5 . I'm using a calculator that is very finicky.
alphysicist
#7
Mar6-09, 01:32 AM
HW Helper
P: 2,249
Quote Quote by number14 View Post
B=3.3*10^-4
I think here you are using N=15; but the B is the magnetic field from the solenoid, which has N=800.
number14
#8
Mar6-09, 01:46 AM
P: 7
thanks so much for the help, i got the right answer finally!!!


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