GRE Reading Comprehension

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Source: 1999

Benjamin Franklin established that lightning is the transfer of positive or negative electrical charge between regions of a cloud or from cloud to earth. Such transfers require that electrically neutral clouds, with uniform charge distributions, become electrified by separation of charges into distinct regions. The greater this separation is, the greater the voltage, or electrical potential of the cloud. Scientists still do not now the precise distribution of charges in thunderclouds nor how separation adequate to support the huge voltages typical of lightning bolts arises. According to one theory, the precipitation hypothesis, charge separation occurs as a result of precipitation. Larger droplets in a thundercloud precipitate downward past smaller suspended droplets. Collisions among droplets transfer negative charge to precipitating droplets, leaving the suspended droplets with a positive charge, thus producing a positive dipole in which the lower region of the thundercloud is filled with negatively charged raindrops and the upper with positively charged suspended droplets.

Question List: 1 2 3 4

According to the passage, Benjamin Franklin contributed to the scientific study of lightning by

  • A testing a theory proposed earlier, showing it to be false, and developing an alternative, far more successful theory of his own
  • B making an important discovery that is still important for scientific investigations of lightning
  • C introducing a hypothesis that, though recently shown to be false, proved to be a useful source of insights for scientists studying lightning
  • D developing a technique that has enabled scientists to measure more precisely the phenomena that affect the strength and location of lightning bolts
  • E predicting correctly that two factors previously thought unrelated to lightning would eventually be shown to contribute jointly to the strength and location of lightning bolts

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