Question: The phonograph disc record was the primary medium used for music reproduction until late in the 20th century, replacing the phonograph cylinder recordwith which it had co-existed from the late 1880s through to the 1920sby the late 1920s. Records retained the largest market share even when new formats such as compact cassette were mass-marketed. By the late 1980s, digital media, in the form of the compact disc, had gained a larger market share, and the vinyl record left the mainstream in 1991. From the 1990s to the 2010s, records continued to be manufactured and sold on a much smaller scale, and were especially used by disc jockeys (DJ)s, released by artists in some genres, and listened to by a niche market of audiophiles. The phonograph record has made a niche resurgence in the early 21st century 9.2 million records were sold in the U.S. in 2014, a 260% increase since 2009. Likewise, in the UK sales have increased five-fold from 2009 to 2014.
Try to answer this question if possible: Approximately how many phonograph records were sold in 2014?
Answer: 9.2 million
Question: Vacuum is space void of matter. The word stems from the Latin adjective vacuus for "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often discuss ideal test results that would occur in a perfect vacuum, which they sometimes simply call "vacuum" or free space, and use the term partial vacuum to refer to an actual imperfect vacuum as one might have in a laboratory or in space. In engineering and applied physics on the other hand, vacuum refers to any space in which the pressure is lower than atmospheric pressure. The Latin term in vacuo is used to describe an object as being in what would otherwise be a vacuum.
Try to answer this question if possible: What type of pressure is less than atmospheric pressure in a vacuum?
Answer: gaseous
Question: Consider a half-wave dipole designed to work with signals 1 m wavelength, meaning the antenna would be approximately 50 cm across. If the element has a length-to-diameter ratio of 1000, it will have an inherent resistance of about 63 ohms. Using the appropriate transmission wire or balun, we match that resistance to ensure minimum signal loss. Feeding that antenna with a current of 1 ampere will require 63 volts of RF, and the antenna will radiate 63 watts (ignoring losses) of radio frequency power. Now consider the case when the antenna is fed a signal with a wavelength of 1.25 m; in this case the reflected current would arrive at the feed out-of-phase with the signal, causing the net current to drop while the voltage remains the same. Electrically this appears to be a very high impedance. The antenna and transmission line no longer have the same impedance, and the signal will be reflected back into the antenna, reducing output. This could be addressed by changing the matching system between the antenna and transmission line, but that solution only works well at the new design frequency.
Try to answer this question if possible: What unit is used to measure current?
Answer: ampere
Question: BeiDou-2 (formerly known as COMPASS) is not an extension to the older BeiDou-1, but rather supersedes it outright. The new system will be a constellation of 35 satellites, which include 5 geostationary orbit satellites for backward compatibility with BeiDou-1, and 30 non-geostationary satellites (27 in medium Earth orbit and 3 in inclined geosynchronous orbit), that will offer complete coverage of the globe.
Try to answer this question if possible: Which system will consist of 40 satellites?
Answer:
unanswerable