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(C) According to Einstein's photoelectric equation, the maximum kinetic energy $K$ of the emitted electrons is given by:$K = \frac{hc}{\lambda} - \phi

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(C) According to Einstein's photoelectric equation, the maximum kinetic energy $K$ of the emitted electrons is given by:$K = \frac{hc}{\lambda} - \phi$When an electron of charge $q$ and mass $m$ moves perpendicular to a magnetic field $B$, it follows a circular path of radius $R$ given by:$R = \frac{mv}{qB} = \frac{\sqrt{2mK}}{qB}$Squaring both sides, we get:$R^2 = \frac{2mK}{q^2 B^2}$Rearranging for $B^2$:$B^2 = \frac{2mK}{q^2 R^2}$Substituting the expression for $K$:$B^2 = \frac{2m}{q^2 R^2} \left( \frac{hc}{\lambda} - \phi \right)$$B^2 = \left( \frac{2mhc}{q^2 R^2} \right) \frac{1}{\lambda} - \left( \frac{2m\phi}{q^2 R^2} \right)$This is an equation of a straight line of the form $y = mx + c$, where $y = B^2$, $x = \frac{1}{\lambda}$, slope $m = \frac{2mhc}{q^2 R^2}$ (positive), and intercept $c = -\frac{2m\phi}{q^2 R^2}$ (negative).Thus, the graph is a straight line with a positive slope and a negative y-intercept. This corresponds to Graph $C$.

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