(i) What is the composition of pencil leads? (ii) How are crucibles made with the help of graphite? (iii) How are crucibles made with the help of graphite? (iv) Why is graphite a more preferred lubricant to the ordinary lubricating oils? (v) What is the role of graphite in nuclear reactor?

(i) What is the composition of pencil leads? (ii) How are crucibles m

1.	(i) What is the composition of pencil leads? (ii) How are crucibles made with the help of graphite? (iii) How are crucibles made with the help of graphite? (iv) Why is graphite a more preferred lubricant to the ordinary lubricating oils? (v) What is the role of graphite in nuclear reactor?
Answer» Solution :(i) Pencil leads are manufactured by mixing graphite with CLAY. (II) The more theamount of clay, the harder is thepencil. (iii) Graphite mixed with FINE clay is moulded and sintered into crucibles of desired size and shape. (iv) Graphite is highly RESISTANT to heat andtherefore used as lubricant in those parts of machinery where HIGH heat is generated due to friction. (v) Graphite is used in nuclear reactors as a moderator to slow down the speed of nueutrons produced due to splitting of theatoms of uranium or thorium.