Photoelectric effect

The photoelectric effect is the emission of electrons or other free carriers when electromagnetic radiation, like light, hits a material. Electrons emitted in this manner can be called photoelectrons; this phenomenon is studied in electronic physics and in fields of chemistry such as quantum chemistry and electrochemistry. According to classical electromagnetic theory, the photoelectric effect can be attributed to the transfer of energy from the light to an electron. From this perspective, an alteration in the intensity of light induces changes in the kinetic energy of the electrons emitted from the metal. According to this theory, a sufficiently dim light is expected to show a time lag between the initial shining of its light and the subsequent emission of an electron, but the experimental results did not correlate with either of the two predictions made by classical theory. Instead, experiments showed that electrons are dislodged only by the impingement of light when it reached or exceeded a threshold frequency.

Below that threshold, no electrons are emitted from the material, regardless of the light intensity or the length of time of exposure to the light. Because a low-frequency beam at a high intensity could not build up the energy required to produce photoelectrons like it would have if light's energy was continuous like a wave, Einstein proposed that a beam of light is not a wave propagating through space, but rather a collection of discrete wave packets. Emission of conduction electrons from typical metals requires a few electron-volts, corresponding to short-wavelength visible or ultraviolet light. Emissions can be induced with photons with energies approaching zero to over 1 MeV for core electrons in elements with a high atomic number. Study of the photoelectric effect led to important steps in understanding the quantum nature of light and electrons and influenced the formation of the concept of wave–particle duality. Other phenomena where light affects the movement of electric charges include the photoconductive effect, the photovoltaic effect, the photoelectrochemical effect.

The photons of a light beam have a characteristic energy, proportional to the frequency of the light. In the photoemission process, if an electron within some material absorbs the energy of one photon and acquires more energy than the work function of the material, it is ejected. If the photon energy is too low, the electron is unable to escape the material. Since an increase in the intensity of low-frequency light will only increase the number of low-energy photons sent over a given interval of time, this change in intensity will not create any single photon with enough energy to dislodge an electron. Thus, the energy of the emitted electrons does not depend on the intensity of the incoming light, but only on the energy of the individual photons, it is an interaction between the innermost electrons. The movement of an outer electron to occupy the vacancy result in the emission of a photon. Electrons can absorb energy from photons when irradiated, but they follow an "all or nothing" principle.

All of the energy from one photon must be absorbed and used to liberate one electron from atomic binding, or else the energy is re-emitted. If the photon energy is absorbed, some of the energy liberates the electron from the atom, the rest contributes to the electron's kinetic energy as a free particle. Photoemission can occur from any material, but it is most observable from metals or other conductors because the process produces a charge imbalance, if this charge imbalance is not neutralized by current flow, the potential barrier to emission increases until the emission current ceases, it is usual to have the emitting surface in a vacuum, since gases impede the flow of photoelectrons and make them difficult to observe. Additionally, the energy barrier to photoemission is increased by thin oxide layers on metal surfaces if the metal has been exposed to oxygen, so most practical experiments and devices based on the photoelectric effect use clean metal surfaces in a vacuum; when the photoelectron is emitted into a solid rather than into a vacuum, the term internal photoemission is used, emission into a vacuum distinguished as external photoemission.

The theory of the source of photoelectric effect must explain the experimental observations of the emission of electrons from an illuminated metal surface. For a given metal surface, there exists a certain minimum frequency of incident radiation below which no photoelectrons are emitted; this frequency is called the threshold frequency. Increasing the frequency of the incident beam, keeping the number of incident photons fixed increases the maximum kinetic energy of the photoelectrons emitted, thus the stopping voltage increases. The number of electrons changes because of the probability that each photon results in an emitted electron are a function of photon energy. If the intensity of the incident radiation of a given frequency is increased, there is no effect on the kinetic energy of each photoelectron. Above the threshold frequency, the maximum kinetic energy of the emitted photoelectron depends on the frequency of the incident light, but is independent of the intensity of the incident light so long as the latter is not too high.

For a given metal and frequency of incident radiation, the rate at which photoelectrons are ejected is directly proportional to the intensity of the incident light. An increase in the intensity of the incident beam increase

Mesilla Plaza

Mesilla Plaza is the central plaza in the small town of Mesilla in far southern New Mexico. The plaza and a number of its surrounding buildings are a National Historic Landmark District, significant for its role in the transfers of power that brought first the original New Mexico Territory and the Gadsden Purchase into United States control; the most notable building facing the plaza is the Basilica of San Albino, on the plaza since its establishment in 1851. The plaza was declared a National Historic Landmark in 1961; the town of Mesilla was created by a Mexican government decree in 1848, as a place to receive Mexican citizens who sought to remain on Mexican soil after the cession of the northern parts of present-day New Mexico were ceded to the United States in the 1848 Treaty of Guadalupe Hidalgo, which ended the Mexican–American War. Just five years the Gadsden Purchase agreement result in the United States purchase of the southern strips of present-day New Mexico and Arizona, an area that includes Mesilla.

The Mesilla Plaza was the site of an official flag-raising ceremony on November 18, 1854, confirming United States sovereignty over the area. The town continued to hold a prominent economic role in territorial affairs, serving as a stop on the Butterfield Overland Mail route, other stagecoach routes, it served as a military center during the American Civil War, at different times for both Union and Confederate forces in the Arizona Territory. Mesilla Plaza was the site of one of the bloodiest political riots in New Mexico history. On August 27, 1871, Democrats held a large political rally in the plaza for their candidate for territorial delegate to the United States Congress. Republicans were holding a rally at a nearby home for their candidate; the Republicans moved from the house to the plaza to disrupt the Democrats' rally. The two groups confronted each other shoving. One man was struck with an axe handle and shooting started. Soldiers from nearby Fort Selden stationed in the town to stop any violence had left earlier when it appeared the rallies were peaceful.

A messenger caught up with the soldiers and they returned to Mesilla. By most of the violence was over. Nine people were killed, an estimated fifty people were injured; the plaza today is still ringed by many buildings harkening back to its early days. The plaza itself an open dirt area, is now lined by brick sidewalks and is grassy, sports a bandstand built in the 1970s; the most prominent structure is the Basilica of San Albino, built in 1906 on the site of the original 1852 church. Buildings on the east and west sides include Territorial style buildings from the 1850s, among them the original Butterfield State ticket office and waiting room; some buildings were built as residences, but have since been readapted for commercial use, while some were built for commercial use. National Register of Historic Places listings in Doña Ana County, New Mexico List of National Historic Landmarks in New Mexico Historic American Buildings Survey No. NM-205, "Barela-Reynolds House, Calle Principal" HABS No.

NM-213, "Iglesia de San Albino, Calle de Santiago" HABS No. NM-214, "Maurin Building, Calle Principal" Historic American Landscapes Survey No. NM-2, "Plaza, Bounded by Calle de Principal, Calle de Parian, Calle de Guadalupe, Calle de Santiago"


Banawadi is a census village of Satara district in the Indian state of Maharashtra. It is situated near to the Satara Phaltan state highway, about 21 km north of Satara, about 108 km from Pune and 220 km from Mumbai. In the 2011 India census, the village of Banawadi had a population of 1,426. Literacy rate of Banawadi village was 91.11% compared to 82.34% of Maharashtra. These forts are well known as dual forts situated in Banawadi village. Based on historical evidences these forts are built by king Bhoj II ruler from Shilahar Dynasty in 1191-1192 B. C. age of copper-inscriptions. In 1673 Shivaji, founder of Maratha Empire conquered it along with other forts in Satara region Ajinkyatara, Kalyangad etc. Maratha ruled these forts till Chatrapati Sambhaji's regime, 1689 Mughals empowered it from Maratha's. After Anglo-Maratha war British took over control of Satara region and hence of Chandan-Vandan. Chandan-Vandan is a sacred/famous place for pilgrims. There is a famous durgah and temple of lord Shiva is situated on top of Chandan fort.

Every year urs-e-shareef is celebrated in remembrance of Gaus Paak Mehboob e Subhani on Chandan fort at banawadi. The post monsoon season is the perfect time to visit these forts; the area is fantastically lush green and excellent visibility too, hard to get in monsoon season. This trek is ideal for those. Bagad is a religious festive tradition, where in ceremonial pole from auspicious tree is venerated in some village jatras in honour of local deities in Maharashtra state of India. Bagad is a similar concept to Charak Puja, Gajan or Indian parallel of Mexican Danza de los Voladores. Since long ago villagers and devotees of Vadhsidhnath from different places celebrating the traditional bagad yatra. Bagad is decorated with coconuts and flowers; this annual festival attracts thousands of devotees during Chaitra month as per traditional Hindu lunar calendar. Rayat Shikshan Sanstha's New English School, Banawadi Z. P. School, Banawadi The best way to reach Banawadi is by road from Satara take public transport bus to Banawadi or any bus going towards Phaltan, get down at Ambawade fata and take local transport for near 4 km.

The alternate way is You may Board train Koyna Express train number 11029. This train runs daily between Mumbai CST to Kolhapur, it departs from Mumbai CST at 08:40 and get down at Wathar Station, get public or local transport from Wathar Station to reach Banawadi. Nearby railway stations are Palashi Station and Mahuli Satara. Nearby airports are Pune. Dudhanwadi Arabwadi Ibrahimpur Ambawade Pimpode Khurd Deur Shivthar Bhuinj Panchwad Palshi Station Satara Road