1 \begin{problem*}{27.17}
2 A portion of Nichrome wire of radius $2.50\U{mm}$ is to be used in
3 winding a heating coil. If the coil must draw a current of
4 $9.25\U{A}$ when a voltage of $120\U{V}$ is applied across its ends,
5 find \Part{a} the required resistance of the coil and \Part{b} the
6 length of wire you must use to wind the coil.
14 R &= \frac{V}{I} = \ans{13.0\U{\Ohm}}
18 Using the formula for conductor resistance
20 R &= \rho \frac{l}{A} \\
21 l &= \frac{RA}{\rho} = \frac{R\pi r^2}{\rho}
24 where the approximate resistivity of Nichrome at $20\celsius$
25 ($\rho=1.00\E{-6}\U{\Ohm$\cdot$m}$) comes from Table~27.2.