In Lenard's experiment, the stopping potential for photoelectrons emitted from a metal surface illuminated by light of wavelength $\lambda_1$ is $V_1$. When the wavelength is changed to $\lambda_2$ ($\lambda_2 > \lambda_1$), the stopping potential becomes $V_2$. If the work function of the metal is $\phi$, which of the following relations is correct?

In Lenard's experiment, the stopping potential for photoelectrons emitted from a metal surface illuminated by light of wavelength $\lambda_1$ is $V_1$. When the wavelength is changed to $\lambda_2$ ($\lambda_2 > \lambda_1$), the stopping potential becomes $V_2$. If the work function of the metal is $\phi$, which of the following relations is correct?

In a photoelectric effect experiment, the slope of the graph between the stopping potential and the incident frequency will be