Equation 26-1 tells us that that a graph of \(K_{\mathrm{max}}\) as a function of the light frequency \(f\) should be a straight line of slope \(h\) (see Figure 26-3). Since kinetic energy can never be negative, Equation 26-1 also tells us that electrons will be emitted only if \(hf - \Phi_0 > 0\).