Calculating Average Induced EMF in a Rotating Coil

[physgrl]

Homework Statement

A flat coil of wire has an area of 0.010 m2and contains 100 turns. Initially the coil is oriented so that the normal to its surface is parallel to a downward constant magnetic field of 0.2 T. The coil is then rotated clockwise through an angle of 30oin a time of 0.10 s. What is the average induced emf? (Note: the initial emf is zero)

a. 0.50 V

b. 0.45 V

*c. 0.18 V

d. 0.25 V

Homework Equations

emf=-Δ$\Phi$_B/Δt
$\Phi$_B=N*ABcos(θ)

The Attempt at a Solution

emf=-Δ$\Phi$_B/Δt
emf=-N*AB(cos(θ₁)-cos(θ₂))/Δt
emf=-100*0.01m²*.2T(cos(0)-cos(30))/.1s
emf=2.7x10^-2V

the answer appears to be .18V...can someone tell me why is this? thanks!

 

[I like Serena]

Hey!

Nope. I can't tell you why that is.
Btw, he answer I get is emf=0.27V, so it seems to me you made a mistake with the power of 10.

In other words IMHO your answer key is wrong!
The right answer isn't even in there.
Is it possible you made a typo when typing down the problem statement?

Anyway, I believe we've given you an answer like this one a couple of times before.
Where do you get your answers?

 

[physgrl]

Hey!
yeah, my answer keys seem to be wrong a lot this is were I study from http://www.montereyinstitute.org/courses/AP%20Physics%20B%20II/nroc%20prototype%20files/coursestartc.html but some answer keys I find here http://bodweb02.bishopodowd.org/UCCP/APPhysicsCII/course%20files/

 

[I like Serena]

So where's this one and its "answer"?

 

[physgrl]

on the first link unit 3>>chapter 14>>lesson 41>> assessments >>answer key >>question 7

 

[I like Serena]

Yep. I see it.
And still no clue why the answer would be wrong.

 

[physgrl]

Oh well :/