Photoelectric Effect Definition and Explanation

The photoelectric effect occurs when matter emits electrons upon exposure to electromagnetic radiation, such as photons of light. Heres a closer look at what the photoelectric effect is and how it works. Overview of the Photoelectric Effect The photoelectric effect is studied in part because it can be an introduction to wave-particle duality and quantum mechanics. When a surface is exposed to sufficiently energetic electromagnetic energy, light will be absorbed and electrons will be emitted. The threshold frequency is different for different materials. It is visible light for alkali metals, near-ultraviolet light for other metals, and extreme-ultraviolet radiation for nonmetals. The photoelectric effect occurs with photons having energies from a few electronvolts to over 1 MeV. At the high photon energies comparable to the electron rest energy of 511 keV, Compton scattering may occur pair production may take place at energies over 1.022 MeV. Einstein proposed that light consisted of quanta, which we call photons. He suggested that the energy in each quantum of light was equal to the frequency multiplied by a constant (Plancks constant) and that a photon with a frequency over a certain threshold would have sufficient energy to eject a single electron, producing the photoelectric effect. It turns out that light does not need to be quantized in order to explain the photoelectric effect, but some textbooks persist in saying that the photoelectric effect demonstrates the particle nature of light. Einsteins Equations for the Photoelectric Effect Einsteins interpretation of the photoelectric effect results in equations which are valid for visible and ultraviolet light: energy of photon energy needed to remove an electron kinetic energy of the emitted electron hÃŽ ½ W E whereh is Plancks constantÃŽ ½ is the frequency of the incident photonW is the work function, which is the minimum energy required to remove an electron from the surface of a given metal: hÃŽ ½0E is the maximum kinetic energy of ejected electrons: 1/2 mv2ÃŽ ½0 is the threshold frequency for the photoelectric effectm is the rest mass of the ejected electronv is the speed of the ejected electron No electron will be emitted if the incident photons energy is less than the work function. Applying Einsteins special theory of relativity, the relationship between energy (E) and momentum (p) of a particle is E [(pc)2 (mc2)2](1/2) where m is the rest mass of the particle and c is the velocity of light in a vacuum. Key Features of the Photoelectric Effect The rate at which photoelectrons are ejected is directly proportional to the intensity of the incident light, for a given frequency of incident radiation and metal.The time between the incidence and emission of a photoelectron is very small, less than 10–9 second.For a given metal, there is a minimum frequency of incident radiation below which the photoelectric effect will not occur, so no photoelectrons can be emitted (threshold frequency).Above the threshold frequency, the maximum kinetic energy of the emitted photoelectron depends on the frequency of the incident radiation but is independent of its intensity.If the incident light is linearly polarized, then the directional distribution of emitted electrons will peak in the direction of polarization (the direction of the electric field). Comparing the Photoelectric Effect With Other Interactions When light and matter interact, several processes are possible, depending on the energy of incident radiation. The photoelectric effect results from low energy light. Mid-energy can produce Thomson scattering and Compton scattering. High energy light can cause pair production.

The Eclipse Of God And The Need For The Jews - 1680 Words

The eclipse of God and the need for the Jews to prove their faith in God stands out as another key response by the Jews. According to Jewish theologians, there are times in the history of religion that God had adamantly refused to show his face to the world. In the Holocaust context, the Jewish theologians argue that God was intentionally absent during this period to test the Jewish and their endurance through suffering. Admittedly, this premise is particularly complex because a section of the theologians has argued that it could be possible that God was seemingly absent because God is a distant God. The premise of the eclipse of God explains why the Jews hold to the belief that God is a distant God who prefers to give human beings a free†¦show more content†¦It shows just how extremely strong they are because I truly don’t know if I would even believe in God or a higher power after the Holocaust. The fact that they are willing to test their faith and provide reasons as to why this happened is really eye opening. I can relate with them on the fact that they think God was absent during this time and that it was meant to make their faith stronger; he would eventually return and all of this madness would end. I also think the Holocaust helped with people’s faith. They were left with no answers for such a tragedy; it was up to them to test their faith and try to figure out exactly why this happened. It made them in my opinion, the strongest believers and observers of if God or a higher power is real. One can think of the Holocaust as a total destroyer of any hope but I believe everyone who lived through this held onto faith/hope and that is the reason why they made it out alive. The United States, Britain as well as the Soviet Union jointly acknowledged the mass murders, but were very reluctant to stop or prevent the innocent deaths. They can be referred to as some of the bystanders. President Roosevelt was worried about the anti-Semitic sentiment in America, the public as well as the congress were against the idea to assist the European Jews. On the other hand, the British feared that it could provoke the Palestinian Arab leaders and, therefore, it remained

African Slaves free essay sample

Is it true to say that Indian Indentures between 1 845 and 1917 was simply another form of slavery? How does the evidence support this statement? Rationale My project will be to examine the lives of Indian Indentured laborers between 1845 and 1917. The reason I am examining their lives is to prove that Indian Indentures was just another form of slavery with a different name. The project will also assist me in learning about the Indian Indentures period for my SEC examination.Introduction Indentured labor was something like the last resort for planters after slavery. After the abolition of slavery the planters were left with a labor shortage. In their search for other sources of labor the planters tried Chinese, Mandarins, even free African slaves but each of these options all had their disadvantages. After a trial and error period with many different laborers, it was found that the Indians were the ideal laborers. The Indentures period was supposed to be a fair, humane and just system unlike the African slave trade and slavery on the whole but this was not the case. We will write a custom essay sample on African Slaves or any similar topic specifically for you Do Not WasteYour Time HIRE WRITER Only 13.90 / page In many aspects of the Indentures period, it was almost identical to slavery. In the following paragraphs it will be shown from the evidence given, that Indians were treated almost as badly as African slaves, proving that the Indentures period was simply another form of slavery. Indentures and slavery are basically the same thing but the major thing that differentiated them was the fact that the Indian laborers were legally owned while the African slaves were forced to work for the planters.The Indians were cheated into signing contracts which they didnt understand with false promises of a better life and good working conditions. The Indians were gullible and were easily tricked into signing the contracts which ran from 3-5 years. The African slaves on the other were kidnapped in most cases and forced to work for the rest of their usually short lives. Their only chance of freedom would be allowed only if they purchased it, which was very unlikely. The journey for both the Africans and the Indians began with a long journey on a boat in deplorable living conditions.For the Indians the journey lasted from 93 to 113 days which was longer than the journey of the Africans which lasted from 6 to 10 weeks. Although both journeys were bad the Middle passage was a little worse than the journey the Indians endured. They were both kept in confined spaces which was unhealthy, especially if kept for long periods of time. Because of their confinement diseases were easily spread and the mortality rate was very high. Life on the plantation was not much different because their living quarter were also confined.