light intensity photoelectric effect equation

The stopping voltage is the potential difference required to prevent photoelectrons from reaching the anode. Thus, only electrons ejected with enough kinetic energy to overcome the work done by the electric field will reach the anode and flow through the galvanometer. To measure the kinetic energy of the ejected electrons, Lenard applied a reverse voltage that does work against the liberated electrons' motion. Measuring the kinetic energy of photoelectrons When there are more photoelectrons reaching the anode, the magnitude of current will increases. When photoelectrons reach the anode, they flow through the wire from the anode back to the cathode. The galvanometer is used to measure the current, which is the amount of charge (electrons) flowing through it per second. The ejected electrons, which are termed photoelectrons, were travelling towards the negatively charged metal (anode). The variable light source was used to illuminate a positively charged metal plate (cathode) in an evacuated tube (vacuum). He also measured the magnitude of current produced by the ejected electrons. In 1902, Hertz's student, Philipp Lenard, studied how the energy of the emitted photoelectrons varied with the intensity and frequency of light. Lenard's Experiment on the Photoelectric Effect Therefore, the wave model of light predicted that electrons will be ejected from a metal regardless of what the intensity or frequency of the light source is. When light of higher intensity (greater power) is used, electrons will take shorter time to receive this sufficient amount of energy and be ejected. Electrons in the metal were ejected when they receive a sufficient amount of energy.

In the wave model, energy is assumed to be continuous. When light of higher frequency is used, the rate at which electrons will be ejected is faster. Therefore, electrons will be ejected with greater kinetic energy when light of higher intensity is used to illuminate a metal surface.įrequency of light is related to the rate of oscillation of light's electric field. Increasing the intensity of light increases the extent of oscillation of electric fields. In the wave model, intensity of light is proportional to the square of its amplitude. Light of any intensity and frequency will be able to eject electrons.Light with higher frequency will result in a greater current.Light with higher intensity will eject electrons with greater kinetic energy.The wave model of light made 3 main predictions regarding the photoelectric effect: Predictions made by the Wave Model of Light The following video discusses how Einstein developed a new model of light – the quantum model, to explain the photoelectric effect. It is important to understand how this classical theory predicted the way in which the number and speed of photoelectrons emitted, along with the time required for their emission, would vary with the intensity and wavelength of the incident light.Įinstein's Explanation of the Photoelectric Effect The ejected electrons are called photoelectrons.

Maxwell's electromagnetic model of light underpinned the classical explanation of the photoelectric effect, where the electrons in the metal atoms were shaken and caused to vibrate by the oscillating electric field of the light.Įventually some of these electrons would be shaken loose and ejected. He discovered that shining UV light on a receiver loop increased the spark length. The photoelectric effect was first observed (but not explained) in 1887 by Heinrich Hertz and is therefore sometimes termed the Hertz effect. Hertz’s Observation of Photoelectric Effect analyse the photoelectric effect K max = hf – φ as it occurs in metallic elements by applying the Law of Conservation of Energy and the photon model of light.investigate the evidence from photoelectric effect investigations that demonstrate inconsistency with the wave model of light (ACSPH087, ACSPH123, ACSPH137).The experimental data in this figure are plotted in arbitrary units so that the height of the profile reflects the intensity of the scattered beam above background noise.This is part of the HSC Physics course under the topic Light: Quantum Model.

Light intensity photoelectric effect equation