The correct option is (c).
Explanation
The historical development of electromagnetism began with observations of static electricity in ancient times. The unification of terrestrial electrical phenomena (like sparks) and atmospheric electrical phenomena (like lightning) was a significant milestone in physics achieved in the 18th century.
Statement-wise Analysis
- Statement 1 is Correct: It is a historically established fact that Thales of Miletus (around 600 BC), an ancient Greek philosopher, observed that amber rubbed with wool or fur acquires the property of attracting light objects such as dry leaves, dust, or hair. The word "electricity" is derived from the Greek word elektron, meaning amber.
- Statement 2 is Incorrect: Benjamin Franklin did not prove they were different; rather, he demonstrated that lightning and the spark generated from amber (or clothes) are essentially the same phenomenon. Through his famous kite experiment in 1752, he established the electrical nature of lightning.
- Statement 3 is Correct: The initial discovery by the Greeks occurred around 600 BC. The realization that the atmospheric lightning and the static sparks produced in laboratories were manifestations of the same underlying principle occurred with Franklin's work in the mid-18th century (1752 AD). This gap spans approximately two thousand years.
Key Takeaway: Static electricity was known to the ancients through the triboelectric effect (rubbing amber), but the unification of this phenomenon with atmospheric lightning was only established by Benjamin Franklin in the 18th century.