Question: In the last two decades, photovoltaics (PV), also known as solar PV, has evolved from a pure niche market of small scale applications towards becoming a mainstream electricity source. A solar cell is a device that converts light directly into electricity using the photoelectric effect. The first solar cell was constructed by Charles Fritts in the 1880s. In 1931 a German engineer, Dr Bruno Lange, developed a photo cell using silver selenide in place of copper oxide. Although the prototype selenium cells converted less than 1% of incident light into electricity, both Ernst Werner von Siemens and James Clerk Maxwell recognized the importance of this discovery. Following the work of Russell Ohl in the 1940s, researchers Gerald Pearson, Calvin Fuller and Daryl Chapin created the crystalline silicon solar cell in 1954. These early solar cells cost 286 USD/watt and reached efficiencies of 4.56%. By 2012 available efficiencies exceed 20% and the maximum efficiency of research photovoltaics is over 40%.
Try to answer this question if possible: In the 1880s, who constructed the first solar cell?
Answer: Charles Fritts
Question: In 1840, Louis Philippe I obtained permission from the British to return Napoleon's remains to France. On 15 December 1840, a state funeral was held. The hearse proceeded from the Arc de Triomphe down the Champs-Elysees, across the Place de la Concorde to the Esplanade des Invalides and then to the cupola in St Jerome's Chapel, where it remained until the tomb designed by Louis Visconti was completed. In 1861, Napoleon's remains were entombed in a porphyry sarcophagus in the crypt under the dome at Les Invalides.
Try to answer this question if possible: On what date was a state funeral held for Napoleon?
Answer: 15 December 1840
Question: The original Latin word "universitas" refers in general to "a number of persons associated into one body, a society, company, community, guild, corporation, etc." At the time of the emergence of urban town life and medieval guilds, specialised "associations of students and teachers with collective legal rights usually guaranteed by charters issued by princes, prelates, or the towns in which they were located" came to be denominated by this general term. Like other guilds, they were self-regulating and determined the qualifications of their members.
Try to answer this question if possible: Around the beginning of what two things did word universitas start to become prevalent?
Answer: urban town life and medieval guilds
Question: In 121 BC, Han forces expelled the Xiongnu from a vast territory spanning the Hexi Corridor to Lop Nur. They repelled a joint Xiongnu-Qiang invasion of this northwestern territory in 111 BC. In that year, the Han court established four new frontier commanderies in this region: Jiuquan, Zhangyi, Dunhuang, and Wuwei. The majority of people on the frontier were soldiers. On occasion, the court forcibly moved peasant farmers to new frontier settlements, along with government-owned slaves and convicts who performed hard labor. The court also encouraged commoners, such as farmers, merchants, landowners, and hired laborers, to voluntarily migrate to the frontier.
Try to answer this question if possible: In what year did Han forces stop a joint Xiongnu-Qiang invasion?
Answer:
111 BC