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Home  >>  JEEMAIN and AIPMT  >>  Physics  >>  Class11  >>  Thermodynamics
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The brass scale of a barometer is correct at $\;0^{0}C\;$ and it reads 755 mm at $\;25^{0}C\;$ , Its reading at $\;0^{0}C\;$ is $\;r_{mercury} = 0.00018/^{0}C\;,r_{brass} =0.00021/^{0}C$

$(a)\;751\;mm\qquad(b)\;755.2\;mm\qquad(c)\;750\;mm\qquad(d)\;757\;mm$

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Answer : $755.2\;mm$
Explanation :
Correct length of mercury column at $\;25^{0}C\;$ = observed length $\;[1+ \alpha_{brass} \bigtriangleup t]$
$= 755 \;[1+ 0.00007 \times 25]$
reading at $\;0^{0}C\;(1+ \alpha_{mercury} \bigtriangleup t) = 755 \;[1+ 0.00007 \times 25]$
reading at $\;0^{0}C\;$ = 755$\; [\large\frac{1+ 0.00007 \times 25}{1+ 0.00006 \times 25}]$
$ = 755 \; [1+ 0.00001 \times 1]$
$ = 755 .2 \;m$m
answered Apr 8, 2014 by yamini.v
 

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