Induced Voltage Equation: Solving for Constant Magnetic Field

AI Thread Summary
The discussion revolves around calculating the induced emf in a circular loop within a magnetic field that is increasing over time. The initial magnetic field is 0.3 T, and it increases by a factor of 2.4 over 13 seconds, leading to confusion about the correct final value. Participants clarify that the final magnetic field should be calculated by multiplying the initial field by 2.4, not simply adding 2.4. The correct approach involves using Faraday's law to find the change in magnetic field over time, leading to the correct induced voltage calculation. Ultimately, the problem highlights the importance of carefully interpreting the wording in physics problems.
laxmaster08
Messages
19
Reaction score
0
I know the equation for emf: -dflux/dt= -dB/dt*A . In my case everything is constant accept the magnetic field and I am unable to find the equation for that. I know that is what dB is for but that simply does not work in this case.

What is the equation for induced voltage, when everything is constant accept the magnetic field.
 
Physics news on Phys.org
laxmaster08 said:
What is the equation for induced voltage, when everything is constant accept the magnetic field.
That is the equation (Faraday's law). What is the exact problem?
 
Doc Al said:
That is the equation (Faraday's law). What is the exact problem?

A circular loop of radius 31 cm is located in the plane of the paper inside a homogeneous magnetic field of 0.3 T pointing into the paper. It is connected in series with a resistor of 289 Ω. The magnetic field is now increased at a constant rate by a factor of 2.4 in 13 s. Calculate the magnitude of the induced emf in the loop during that time.

I have been using Faraday's. So far I've tried [(2.4-0.3)/13)*pi(.31)^2], [(2.4+0.3)/13)*A], and [(2.4/13)*A]. All in magnitude form.
 
Last edited:
laxmaster08 said:
The magnetic field is now increased at a constant rate by a factor of 2.4 in 13 s.
What's the initial magnetic field before it starts increasing? What's the final magnetic field after 13 seconds? The change in magnetic field during that time?
 
Doc Al said:
What's the initial magnetic field before it starts increasing? What's the final magnetic field after 13 seconds? The change in magnetic field during that time?

2.4-0.3=2.1
According to Faraday this divided by the time ,t=13s, all multiplied by the area, A=pi*(.31)^2, should equal the EMF but LON-CAPA does not agree.
Am I missing something? it seems pretty straight forward but it isn't coming out right. btw my answer was 0.0488V
 
laxmaster08 said:
2.4-0.3=2.1
According to Faraday this divided by the time ,t=13s, all multiplied by the area, A=pi*(.31)^2, should equal the EMF but LON-CAPA does not agree.
Am I missing something? it seems pretty straight forward but it isn't coming out right. btw my answer was 0.0488V
You are misreading the problem statement. 2.4 is not the final magnetic field, but the factor by which the field is increasing. So once again: What's the final magnetic field after 13 seconds?
 
doc al said:
you are misreading the problem statement. 2.4 is not the final magnetic field, but the factor by which the field is increasing. So once again: What's the final magnetic field after 13 seconds?

2.7 ill see if it works
 
laxmaster08 said:
2.7 ill see if it works
No. Show how you made that calculation.

FYI: Factor means multiply. If you start out weighing 150 lbs and your weight increases by a factor of 2, what's your final weight?
 
Doc Al said:
You are misreading the problem statement. 2.4 is not the final magnetic field, but the factor by which the field is increasing. So once again: What's the final magnetic field after 13 seconds?

Ok that didnt work. So the way its worded it looks like the total time it takes to charge up 2.4 is 13s but I guess it could mean that it charges up 2.4 every second for 13s...Ill try it
 
  • #10
laxmaster08 said:
Ok that didnt work. So the way its worded it looks like the total time it takes to charge up 2.4 is 13s but I guess it could mean that it charges up 2.4 every second for 13s...Ill try it
Nope. Reread my last comment.
 
  • #11
Doc Al said:
Nope. Reread my last comment.

Ok so I am going to multiply my initial 0.3 by a factor of 2.4?
 
  • #12
*over a time period of 13s
 
  • #13
laxmaster08 said:
Ok so I am going to multiply my initial 0.3 by a factor of 2.4?
Yes. At least I hope so!
 
  • #14
nope
 
  • #15
Any ideas? Faraday doesn't say anything about resistance so I'm guessing that pertains to part b of the problem...
 
  • #16
laxmaster08 said:
nope
Nope what?
 
  • #17
Doc Al said:
Nope what?

That doesn't work.
 
  • #18
laxmaster08 said:
That doesn't work.
Show what you did.
 
  • #19
Doc Al said:
Show what you did.

(2.4*0.3)/13)*pi*(.31)^2=0.0167V
 
  • #20
laxmaster08 said:
(2.4*0.3)/13)*pi*(.31)^2=0.0167V
You need the change in magnetic field over time, not just the final field.
 
  • #21
Doc Al said:
You need the change in magnetic field over time, not just the final field.

dB/dt=(2.4-0.3)/(13) ?
 
  • #22
or (2.4*0.3)-(0.3))/13
 
  • #23
Success! That problem had really sneaky wording.
 
  • #24
laxmaster08 said:
Success! That problem had really sneaky wording.
Finally! :cool:
 
  • #25
Now the second part looks much trickier. It looks like I will have to use right hand rule...
"Calculate the average induced voltage when the magnetic field is constant at 0.72 T while the loop is pulled horizontally out of the magnetic field region in 4.1 s"
 
  • #26
Haha yah that took quite a while. If your out ill understand I can probably figure this one out...probably.
 
  • #27
What does it mean by pulled out of the magnetic field? Does that mean a force due to current in the loop is pushing it?
 
  • #28
Will this use Faraday's?
 
  • #29
Nvm that was cake! thanks man peace out
 

Similar threads

B EMF induced by Bar Magnet falling through a Coil
Replies
3
Views
535
B Magnet inside a solenoid with current
Replies
7
Views
1K
B Why does accelerating a loop through a constant magnetic field induce an EMF?
Replies
9
Views
2K
B How do you calculate induced EMF in an open loop with changing magnetic field?
Replies
4
Views
3K
I Pushing a rod in a magnetic field
Replies
15
Views
2K
Calculating Induced EMF in Moving Wire
Replies
11
Views
6K
B The factors determining the induced EMF in a wire
Replies
6
Views
4K
I Induced electric fields and induced magnetic fields confusion
Replies
9
Views
3K
B What would happen if there were no back EMF in an electric motor?
Replies
10
Views
2K
Using Faraday's laws to find the induced EMF
Replies
3
Views
2K

Hot Threads

Recent Insights

Back
Top