Problem: Motors have very little room for electrical insulation so they generally have low voltage ratings. Because transformers (prior to the development of power electronics) cannot step down DC voltages, trains were supplied with a relatively low DC voltage that the motors can use directly. The most common DC voltages are listed in the previous section. Third (and fourth) rail systems almost always use voltages below 1 kV for safety reasons while overhead wires usually use higher voltages for efficiency. ("Low" voltage is relative; even 600 V can be instantly lethal when touched.)
What is most common volatage range used by railway system?
The answer is the following: below 1 kV

Problem: New Delhi has been selected as one of the hundred Indian cities to be developed as a smart city under PM Narendra Modi's flagship Smart Cities Mission.
Who is responsible for India's smart city initiative?
The answer is the following: PM Narendra Modi

Problem: LaserDiscs were initially cheaper than videocassettes to manufacture, because they lacked the moving parts and plastic outer shell that are necessary for VHS tapes to work, and the duplication process was much simpler. A VHS cassette has at least 14 parts including the actual tape while LaserDisc has one part with five or six layers. A disc can be stamped out in a matter of seconds whereas duplicating videotape required a complex bulk tape duplication mechanism and was a time-consuming process. However, by the end of the 1980s, average disc-pressing prices were over $5.00 per two-sided disc, due to the large amount of plastic material and the costly glass-mastering process needed to make the metal stamper mechanisms. Due to the larger volume of demand, videocassettes quickly became much cheaper to duplicate, costing as little as $1.00 by the beginning of the 1990s.
How much did LaserDiscs cost to produce by the end of the 1980s?
The answer is the following: $5.00 per two-sided disc

Problem: Tucson's primary electrical power source is a coal and natural gas power-plant managed by Tucson Electric Power that is situated within the city limits on the south-western boundary of Davis-Monthan Air-force base adjacent to Interstate-10. The air pollution generated has raised some concerns as the Sundt operating station has been online since 1962 as is exempt from many pollution standards and controls due to its age. Solar has been gaining ground in Tucson with its ideal over 300 days of sunshine climate. Federal, state, and even local utility credits and incentives have also enticed residents to equip homes with solar systems. Davis-Monthan AFB has a 3.3 Megawatt (MW) ground-mounted solar photovoltaic (PV) array and a 2.7 MW rooftop-mounted PV array, both of which are located in the Base Housing area. The base will soon have the largest solar-generating capacity in the United States Department of Defense after awarding a contract on September 10, 2010, to SunEdison to construct a 14.5 MW PV field on the northwestern side of the base.
When did Tucson's main power plant begin operation?
The answer is the following:
1962