- #1

NoPhysicsGenius

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## Homework Statement

The following is Problem 1-13 on page 23 from Electrical Engineering Fundamentals, 2nd ed., by Vincent del Toro:

"In the configuration shown in Fig. P1-13 the coil has 100 turns and is attached to the rotating member which revolves at 25 [itex]\frac{rev}{s}[/itex]. The magnetic flux is a radial uniform field and has a value of [itex]\phi = 0.002 weber (Wb)[/itex]. Compute the emf induced in the coil."

Here is Fig. P1-13 ...

http://www.flickr.com/photos/jjhobson/8005932239/in/photostream

## Homework Equations

[tex]e = - \frac{d\lambda}{dt} = -N\frac{d\phi}{dt}[/tex]

Note that e stands for emf (or electromotive force), [itex]\lambda[/itex] stands for the flux linkage in weber-turns, N stands for the number of turns in the coil, and [itex]\phi[/itex] stands for the magnetic flux.

## The Attempt at a Solution

First of all, the answer given in the back of the book is

**20 Volts**.

[tex]e = -N\frac{d\phi}{dt} = -(100)\frac{d\phi}{dt}[/tex]

[tex]\Rightarrow \frac{d\phi}{dt} = -\frac{e}{100}[/tex]

[tex]\Rightarrow d\phi = -\frac{e}{100}dt[/tex]

[tex]\Rightarrow \phi = -\frac{1}{100}\int e dt = 0.002 Wb[/tex]

[tex]\Rightarrow \int e dt = -0.2 Wb[/tex]

Unfortunately, I don't know where to go from here. Also, I don't know where the 25 rev/s quantity comes into play.

Any help would be greatly appreciated. Thank you.