# A Hole is Drilled in a Copper Sheet. the Diameter of the Hole is 4.24 Cm at 27.0 °C. What is the Change in the Diameter of the Hole When the Sheet is Heated to 227 °C? Coefficient of Linear Expansion of Copper = 1.70 × 10–5 K–1. - Physics

A hole is drilled in a copper sheet. The diameter of the hole is 4.24 cm at 27.0 °C. What is the change in the diameter of the hole when the sheet is heated to 227 °C? Coefficient of linear expansion of copper = 1.70 × 10–5 K–1.

#### Solution 1

Initial temperature, T1 = 27.0°C

Diameter of the hole at T1d1 = 4.24 cm

Final temperature, T2 = 227°C

Diameter of the hole at Td2

Co-efficient of linear expansion of copper, αCu= 1.70 × 10–5 K–1

For co-efficient of superficial expansion β,and change in temperature ΔT, we have the relation:

"Change in area(ΔA)"/"Original area(A)" = betaΔT

(((pi (d_2^2))/4 - pi (d_1^2)/4))/((pi d_1^2/4)) = (triangleA)/A

:.(triangleA)/A = (d_2^2 - d_1^2)/d_1^2

But beta = 2 alpha

:.(d_2^2-d_1^2)/d_1^2 =  2alpha triangleT

d_2^2/d_1^2 - 1=  2alpha (T_2 - T_1)

d_2^2/(4.24)^2 = 2xx 1.7 xx10^(-5)(227- 27) + 1

d_2^2 = 17.98 xx 1.0068 = 18.1

:. d_2 = 4.2544 cm

Change in diameter = d2 – d= 4.2544 – 4.24 = 0.0144 cm

Hence, the diameter increases by 1.44 × 10–2 cm.

#### Solution 2

In this  superficial expansion of copper sheet will be involved on heating

Here, area of hole at 27^@, A_1 = piD_1^2/4  = pi/4 xx(4.24)^2 cm^2

if D_2 cm is the diameter of the hole at 227^@C then area of the hole at 227^@C

A_2 =  (piD_2^2)/4 cm^2

Coefficient of superficial expansion of copper is

beta = 2 alpha = 2xx1.70 xx 10^(-5) = 3.4 xx 10^(-5)"'^@C^(-1)

Increase in area  =  A_2 - A_1 =  betaA_1triangleT or A_2 =  A_1 +betaA_1 triangle T =  A_1(1 + beta triangleT)

(piD_2^2)/4 =  pi/4(4.24)^2 [1+3.4xx10^(-5)(228 - 27)]

=> D_2^2 = (4.24)^2xx 1.0068 or

D_2 = 4.2544 cm

Change4 in diameter =  D_2 - D_1  = 4.2544 - 4.24 = 0.0114 cm

Is there an error in this question or solution?

#### APPEARS IN

NCERT Class 11 Physics Textbook
Chapter 11 Thermal Properties of Matter
Q 8 | Page 295