## College Physics (4th Edition)

The correct answer is: (c) $\frac{hc}{\phi}$
If the work function is $\phi$, we can find an expression for the threshold wavelength: $hf = \phi$ $\frac{hc}{\lambda} = \phi$ $\lambda = \frac{hc}{\phi}$ The correct answer is: (c) $\frac{hc}{\phi}$