Thermal Properties of Matter

Question : 7

Total: 22

A large steel wheel is to be fitted on to a shaft of the same material. At 27°C, the outer diameter of the shaft is 8.70 cm and the diameter of the central hole in the wheel is 8.69 cm. The shaft is cooled using ‘dry ice’. At what temperature of the shaft does the wheel slip on the shaft? Assume coefficient of linear expansion of the steel to be constant over the required temperature range : αsteel=1.20×10–5K–1.

Solution:

Here, T1=27°C=27+273=300K
Let L1 and L2 be the linear dimensions of steel at temperatures T1 and T2 respectively.
Now L1=8.70cm,L2=8.69cm, αsteel=1.20×10–5K–1
Change in length =L2−L1=L1α(T2−T1)

8.69–8.70=8.70×(1.20×10–5)×(T2–300)

(T2−300)=

0.01

8.70×1.2×10−5

=−95.78K

T2=300−95.78K=204.22K=−68.93°C

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