Question

(A) A platinum wire can be sealed through a glass. But a brass one cannot be sealed through a glass.
(B) Coefficient of linear expansion of platinum and that of brass have different values.
A. A and B are correct and B is the correct explanation for A.
B. A and B are correct and B is not the correct explanation for A.
C. A is true and B is false.
D. A is wrong and B is true.

Answer 1

Coefficient of linear expansion is the rate at which the length of a material changes with unit increase in temperature. If two materials have the same coefficient of linear expansion, they both will expand at the same rate. While making a seal if the material used to seal and the material taken inside does not have the same coefficient of linear expansion the seal will break when heated.

Complete step by step answer:
We know that different materials expand at different rates when it is heated.
The extent of linear expansion is denoted using the coefficient of linear expansion. Coefficient of linear expansion is the rate at which a material of unit length expands when temperature is changed by one degree.
For a good seal of glass, the material taken inside and the glass should have almost the same coefficient of linear expansion so that when heat is provided both expand to the same extent that the seal will not break. If the material inside expands at a different rate, then there is a chance that the seal will break when heated. So, whenever we need to seal a material using glass, we should make sure that both have similar coefficients of linear expansion. Platinum and glass have the same coefficient of linear expansion. Hence, it can be sealed with glass. But in the case of brass and glass the coefficient of linear expansion of brass is greater than that of glass. So, if heat is provided brass will expand more than glass. This will result in the breakage of the glass.
Hence, A is true. Platinum can be sealed through glass and brass cannot be sealed through glass.
B is also correct because coefficients of linear expansion of platinum and brass are different.
But B is not a correct explanation for A.
Hence option b is the correct answer.

Note: Always remember that when a good seal is needed between material and glass, we should choose the material having the same or almost same coefficient of linear expansion. In electric bulbs we use Platinum sealed with glass. Even when the bulb gets heated the seal will not break since both glass and platinum expand at the same rate. We cannot use glass to seal brass, copper, lead etc. which have a higher coefficient of linear expansion than glass.