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A blacksmith heated a metal whose cubic expansivity is 6....

A blacksmith heated a metal whose cubic expansivity is 6.3 x 10-6K-1. The area expansivity is

A.

2.0 x 10-6K-1

B.

2.1 x 10-6K-1

C.

4.2 x 10-6K-1

D.

6.3 x 10-6K-1

Correct answer is C

If the lineal expansivity = ∝
=> area expansivity β= 2∝.
And cubic expansivity δ = 3∝.
=> 6.3 x 10-6 = 3∝
∴ ∝ =

∴ ∝ = 6.3 x 10-6 = 2.1x 10-6
__3


∴ Area = 2∝ = 2 x 2.1x10-6
= 4.2 x 10-6K-1