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How did Archimedes detect impurity in the golden crown?

Archimedes — an ancient Greek physicist and mathematician — is considered as the ‘Father of Experimental Science‘. He was born at Syracuse in Sicily in the year 287 B.C. and educated in Alexandria. Several principles of science discovered by him such as the ‘law of levers’, ‘laws of flotation’, etc. are taught in schools, even now. But he is more famous for the ‘Archimedes’ Principle’, which tells us when an object is weighed in air and then weighed submerged in a liquid, it will lose weight equal to the weight of the liquid it displaces. There is an interesting and humorous story behind the discovery of this Archimedes Principle. Once, King Hieron of Syracuse gave him a crown made of gold and told him to test its purity without causing any damage to it. The king suspected that the crown was alloyed with silver. The complex problem set Archimedes thinking seriously. How could he test the purity without harming the crown? One day as he entered his bathtub, he found that his body had displaced some water resulting in a small rise in the water level in the tub. He immediately jumped out and ran down the street, naked, shouting “Eureka!” (“I have found it! I have found it!”). Armed with newfound knowledge, he filled a vessel with water and dipped the crown in it. Then he measured the water displaced by it. Next, Archimedes dipped an equal mass of pure gold in water and measured the amount of water displaced. The amount of water displaced in the two observations was different. From this experiment he estimated the impurity in the gold crown. On the basis of this discovery, he gave the method of finding out the relative density of different substances. Archimedes also postulated the laws of floatation of bodies and the principle of levers. He was the first to calculate the value of pi (π). In addition to these, he discovered the use of levers and pulleys and how to pump water uphill using Archimedean screw – a system still in use to irrigate fields in Egypt. He also designed war machines. Though Archimedes lived a good life and did excellent work in sciences, his death was tragic. When Romans conquered Syracuse in 212 B.C., Archimedes had grown old. One day while he was drawing some geometrical figure on sand, a Roman soldier asked him to accompany him. When Archimedes refused, the enraged soldier pulled out his sword and killed him. He was cremated with great honours.

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