- #1

mnafetsc

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## Homework Statement

An open plastic soda bottle with an opening diameter of 2.7 cm is placed on a table. A uniform 1.95-{\rm T} magnetic field directed upward and oriented 21^\circ from vertical encompasses the bottle.

What is the total magnetic flux through the plastic of the soda bottle?

## Homework Equations

flux=B*A*cos[tex]\theta[/tex]

## The Attempt at a Solution

I have the correct answer, but I don't understand why it is negative instead of positive, or in other words why to i subtract 21 from 180, instead of just plugging in 21 into cosine.