What Is the Induced EMF in a Circular Coil at t = 5 s?

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Homework Help Overview

The problem involves calculating the induced electromotive force (EMF) in a circular coil placed in a time-varying magnetic field. The coil has 35 turns and a diameter of 19 cm, and the magnetic field is defined as B(t) = 6 t^2 + 6 t + 2 T. The inquiry focuses on determining the induced EMF at t = 5 seconds.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the relationship between EMF and the rate of change of magnetic flux, with some attempting to apply the formula E = -d(magnetic flux)/dtime. There are questions regarding the correctness of calculations and the implications of negative voltage.

Discussion Status

Some participants have provided guidance on the calculations, including the need to use the radius instead of the diameter for area calculations and to ensure proper unit conversions. There is ongoing exploration of the problem, with no explicit consensus reached.

Contextual Notes

Participants note the importance of unit conversion and the correct interpretation of the formula for induced EMF. There is a sense of urgency as one participant mentions a time constraint for completing the homework.

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Homework Statement

A circular coil with 35 turns of wire and a diameter of 19 cm is placed in a magnetic field given by B(t) = 6 t^2 + 6 t + 2 T where t is time in seconds. The field is perpendicular to the plane of the coil. What is the induced EMF at t = 5 s?

Homework Equations

E=-d(magnetic flux)/dtime

The Attempt at a Solution


I found E to be 36.12 V but that's wrong. I'm not sure what's wrong. I did E=NAB/time.
 
Last edited:
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Emf is proportional to negative the derivative or rate of change of the magnetic flux with respect to time. The area is constant, thus
V = -NA*dB/dt.
 
I plugged in -36.12 but it's still wrong. Can we have a negative voltage?
 
Could you please tell me where I'm wrong? I have a couple of hours left.
 
dB/dt = 12t + 6; at t = 5s, dB/dt = 66T/s
N = 35 turns
A = pi*r^2...so your problem might be that you're using the diameter of 19cm instead of the radius; also, be sure that you convert the given units to the proper units, so the radius = d/2 = 9.5cm = .095m.
The emf is V = -NA*dB/dt...and you could have a negative voltage.
 
Thank you very much I appreciate it.
 

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