How does the electric force between two charged particles change if the distance between them is increased by a factor of 2?
a. it is decreases by a factor of 2
b. it is increases by a factor of 2
c. it is increases by a factor of 4
d. it is decreases by a factor of 4

Year  1936,  lehman predicted that the earths 'inner core' is solid. she observed that the seismic signals during her study were bent and did not pass through instead bouncing back. later it was confirmed that the earth's inner core was solid made up of nickel-iron and had a molten outer core.