First slide

Thermal expansion

Question

PQR is a right angled triangle made of brass rod bent as shown. If it is heated to a high temperature the angle PQR.

Moderate

A

increases
B

decreases
C

remains same
D

becomes 1350

Solution

Suppose, PQ = a, QR = b and PR = c.
$\therefore {a^2} + {b^2} = {c^2}$
It t be the rise in temperature, then a' = a(1+αt), b' = b(1+ $α$ t) and c' = c(1+ $α$ t).
Now, (a')² + (b')²
= {a(1+αt)}²+{b(1+αt)}²
= (a²+b²)(1+αt)²
= c²(1+αt)² = (c')²
So option (3) is right.

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