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Thermal Properties of Matter

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Question : 8 of 22
Marks: +1, -0
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 =1.70×105K1.= 1.70 \times 10^{-5} \mathrm{K}^{-1}.
Solution:  
Here, Coefficient of linear expansion of copper, α=1.70×105K1\alpha = 1.70 \times 10^{-5} \mathrm{K}^{-1}
ΔT=22727=200C\Delta T = 227 - 27 = 200^{\circ}\mathrm{C}
Therefore, coefficient of superficial expansion of copper
β=2α=2×1.70×105K1\beta = 2\alpha = 2 \times 1.70 \times 10^{-5} \mathrm{K}^{-1}
β=3.40×105K1\beta = 3.40 \times 10^{-5} \mathrm{K}^{-1}
Area of hole at 27°C,
S1=πD124=π4(4.24)2 cm2S_{1}= \frac{\pi D_{1}^{2}}{4}= \frac{\pi}{4}(4.24)^{2} \ \mathrm{cm}^{2}
=π×4.4944 cm2=\pi \times 4.4944 \ \mathrm{cm}^{2}
If D2D_2 cm is the diameter of the hole at 227C227^{\circ}\mathrm{C}, then Area of the hole at 227C227^{\circ}\mathrm{C},
S2=πD224 cm2S_{2}= \frac{\pi D_{2}^{2}}{4} \ \mathrm{cm}^{2}
Increase in area =S2S1=S1βΔT=S_{2}-S_{1}=S_{1} \beta \Delta T
S2=S1+S1βΔTS_{2}=S_{1}+S_{1} \beta \Delta T
S2=S1(1+βΔT)\Rightarrow S_{2}=S_{1}(1+\beta \Delta T)
πD224=π×4.4944×(1+3.4×105(22727))\frac{\pi D_{2}^{2}}{4}=\pi \times 4.4944 \times (1+3.4 \times 10^{-5}(227-27) )
D22=(4.24)2×(1.0068)D_{2}^{2}=(4.24)^{2} \times (1.0068)
D2=4.2544 cm\Rightarrow D_{2}=4.2544 \ \mathrm{cm}
Change in diameter =D2D1=D_{2}-D_{1}
=4.25444.24=4.2544-4.24
=0.0144 cm=0.0144 \ \mathrm{cm}
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