Stopping Potential And Maximum Kinetic Energy

The stopping potential $V_0$ is the minimum negative voltage on the collector that turns back even the fastest photoelectrons, reducing the photocurrent to zero. At this point the work done by the retarding field on an electron exactly equals the electron's maximum kinetic energy, so $e{V}_0=K_{max}$. Expressed in electron-volts, the maximum kinetic energy is numerically equal to the stopping potential in volts, because one electron-volt is by definition the energy gained by one electronic charge moving through one volt. Hence $K_{max}=1.5\text{eV}$. The value $3.0\text{eV}$ wrongly doubles the result. The value $0.75\text{eV}$ halves it. The value $2.4\times 10^{-19}\text{eV}$ confuses joules with electron-volts, since $1.5\text{eV}=2.4\times 10^{-19}\text{J}$, not eV. This direct correspondence between stopping potential and electron energy is a cornerstone of the photoelectric measurements described in NCERT. As a unit check, the eV scale keeps numbers convenient and confirms the answer's consistency.