Context and question: The southern Essonne department specialises in science and technology, and the south-eastern Val-de-Marne, with its wholesale Rungis food market, specialises in food processing and beverages. The Paris region's manufacturing decline is quickly being replaced by eco-industries: these employ about 100,000 workers. In 2011, while only 56,927 construction workers worked in Paris itself, its metropolitan area employed 246,639, in an activity centred largely around the Seine-Saint-Denis (41,378) and Hauts-de-Seine (37,303) departments and the new business-park centres appearing there.
How many construction workers worked in Paris in 2011?
Answer: 56,927
Context and question: A synchronous electric motor is an AC motor distinguished by a rotor spinning with coils passing magnets at the same rate as the AC and resulting magnetic field which drives it. Another way of saying this is that it has zero slip under usual operating conditions. Contrast this with an induction motor, which must slip to produce torque. One type of synchronous motor is like an induction motor except the rotor is excited by a DC field. Slip rings and brushes are used to conduct current to the rotor. The rotor poles connect to each other and move at the same speed hence the name synchronous motor. Another type, for low load torque, has flats ground onto a conventional squirrel-cage rotor to create discrete poles. Yet another, such as made by Hammond for its pre-World War II clocks, and in the older Hammond organs, has no rotor windings and discrete poles. It is not self-starting. The clock requires manual starting by a small knob on the back, while the older Hammond organs had an auxiliary starting motor connected by a spring-loaded manually operated switch.
How is current brought to the rotor in a synchronous motor?
Answer: Slip rings and brushes
Context and question: By the end of the decade a distinct genre of hard rock was emerging with bands like Led Zeppelin, who mixed the music of early rock bands with a more hard-edged form of blues rock and acid rock on their first two albums Led Zeppelin (1969) and Led Zeppelin II (1969), and Deep Purple, who began as a progressive rock group but achieved their commercial breakthrough with their fourth and distinctively heavier album, In Rock (1970). Also significant was Black Sabbath's Paranoid (1970), which combined guitar riffs with dissonance and more explicit references to the occult and elements of Gothic horror. All three of these bands have been seen as pivotal in the development of heavy metal, but where metal further accentuated the intensity of the music, with bands like Judas Priest following Sabbath's lead into territory that was often "darker and more menacing", hard rock tended to continue to remain the more exuberant, good-time music.
What is one band directly influenced by Black Sabbath?
Answer:
Judas Priest