GRE Reading Comprehension
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.
The passage is primarily concerned with discussing which of the following?
- A A central issue in the explanation of how lightning occurs
- B Benjamin Franklin's activities as a scientist
- C Research into the strength and distribution of thunderstorms
- D The direction of movement of electrical charges in thunderclouds
- E The relation between a cloud's charge distribution and its voltage
Correct Answer: A