Question: In 1886, Frank Julian Sprague invented the first practical DC motor, a non-sparking motor that maintained relatively constant speed under variable loads. Other Sprague electric inventions about this time greatly improved grid electric distribution (prior work done while employed by Thomas Edison), allowed power from electric motors to be returned to the electric grid, provided for electric distribution to trolleys via overhead wires and the trolley pole, and provided controls systems for electric operations. This allowed Sprague to use electric motors to invent the first electric trolley system in 1887–88 in Richmond VA, the electric elevator and control system in 1892, and the electric subway with independently powered centrally controlled cars, which were first installed in 1892 in Chicago by the South Side Elevated Railway where it became popularly known as the "L". Sprague's motor and related inventions led to an explosion of interest and use in electric motors for industry, while almost simultaneously another great inventor was developing its primary competitor, which would become much more widespread. The development of electric motors of acceptable efficiency was delayed for several decades by failure to recognize the extreme importance of a relatively small air gap between rotor and stator. Efficient designs have a comparatively small air gap. [a] The St. Louis motor, long used in classrooms to illustrate motor principles, is extremely inefficient for the same reason, as well as appearing nothing like a modern motor.
Is there an answer to this question: What needs to exist between the rotor and stator for increased efficiency?

Answer: small air gap


Question: Since 1934, the sale of Federal Duck Stamps has generated $670 million, and helped to purchase or lease 5,200,000 acres (8,100 sq mi; 21,000 km2) of habitat. The stamps serve as a license to hunt migratory birds, an entrance pass for all National Wildlife Refuge areas, and are also considered collectors items often purchased for aesthetic reasons outside of the hunting and birding communities. Although non-hunters buy a significant number of Duck Stamps, eighty-seven percent of their sales are contributed by hunters, which is logical, as hunters are required to purchase them. Distribution of funds is managed by the Migratory Bird Conservation Commission (MBCC).
Is there an answer to this question: How much land has the Duck Stamp Act help purchase?

Answer: 5,200,000 acres


Question: The city has a particular connection to Cunard Line and their fleet of ships. This was particularly evident on 11 November 2008 when the Cunard liner RMS Queen Elizabeth 2 departed the city for the final time amid a spectacular fireworks display after a full day of celebrations. Cunard ships are regularly launched in the city, for example Queen Victoria was named by HRH The Duchess of Cornwall in December 2007, and the Queen named Queen Elizabeth in the city during October 2011. The Duchess of Cambridge performed the naming ceremony of Royal Princess on 13 June 2013.
Is there an answer to this question: In what year did the Queen Elizabeth receive its name from the Queen?

Answer: 2011


Question: The first lighting used on an airport was during the latter part of the 1920s; in the 1930s approach lighting came into use. These indicated the proper direction and angle of descent. The colours and flash intervals of these lights became standardized under the International Civil Aviation Organization (ICAO). In the 1940s, the slope-line approach system was introduced. This consisted of two rows of lights that formed a funnel indicating an aircraft's position on the glideslope. Additional lights indicated incorrect altitude and direction.
Is there an answer to this question: When was the slope-line approach system introduced?

Answer:
1940s