# Maxwell the electric field points toward the cathode, i.e.,

Maxwell formulated the wave nature of light, two decades before the photoelectric effect was observed. the question here is that whether photoelectric effect consistent with this model or not? In photoelectric effect, two conducting electrodes are enclosed in an evacuated glass tube and connected by a battery, and the cathode is then illuminated. Depending on the potential difference V between the two electrodes, electrons emitted by the illuminated cathode (photoelectrons) may travel across to the anode which produce a photocurrent in the external circuit. (The tube has a pressure of 0.01 Pa or less to prevent any collisions between the electrons and gas molecules which cannot be achieved by 100%). The illuminated cathode always emits photoelectrons with various kinetic energies. If the electric field points toward the cathode, i.e., from positive terminal to negative terminal as shown in the figure 1, all the electrons are accelerated toward the anode and contribute to the photocurrent.  Figure 1  But by reversing the field and adjusting its strength as shown in Figure 2, we can prevent the less energetic electrons from reaching the anode.   Figure 2 In fact, we can determine the maximum kinetic energy K max of the emitted electrons by making the potential of the anode relative to the cathode, V, just negative enough so that the current stops. This occurs for V = – Vo. This Vo here is called the stopping potential. As an electron moves from the cathode to the anode, the potential decreases by Vo and negative work -eVo is done on the electron. The most energetic electron leaves the cathode with kinetic energy  and has zero kinetic energy at the anode. So, Initial K.E is  and final K.E is zero. The Work that needs to be done for this change in K.E,  Or,  Or,  Hence, by measuring Vo, we can actually calculate the maximum velocity with which a photoelectron can be emitted. Here the effects due to difference of materials of cathode and anode are neglected here. According to Maxwell’s explanation of light as an electromagnetic wave, the intensity of an electromagnetic wave depends on its amplitude but independent on its frequency. But experimental results show contradiction to this. Actually, the photocurrent does depend on the frequency of the incident light and not on its intensity and there is a certain frequency of the incident light on a metal, below which there is effectively no emission of photoelectron takes place. This frequency is known as the threshold frequency.