1.

Explain linear expansion .

Answer» <html><body><p></p>Solution :Increase in length of substance `(Deltal)` is directly proportional to original length ..l.. and increase in <a href="https://interviewquestions.tuteehub.com/tag/temperature-11887" style="font-weight:bold;" target="_blank" title="Click to know more about TEMPERATURE">TEMPERATURE</a> `..DeltaT..`, <br/> `:.Deltalalphal" and "Deltal alphaDeltaT` <br/> `:.DeltalalphalDeltaT` (combinely) <br/> `:.(Deltal)/(l)alphaDeltaT` <br/> Hence, the fractional change in length. `((Deltal)/(l))` is directly proportional to `DeltaT`. <br/> `:.(Deltal)/(l)propDeltaT` <br/> `:.(Deltal)/(l)=alpha_(l)DeltaT` <br/> `:.Deltal=alpha_(l)lDeltaT` . . . . (1) <br/> Where `alpha_(l)` is coefficient of linear expansion and is characteristic of material. <br/> Value of `alpha_(l)` depends on type of material and temperature. <br/> If the temperature difference is not <a href="https://interviewquestions.tuteehub.com/tag/large-1066424" style="font-weight:bold;" target="_blank" title="Click to know more about LARGE">LARGE</a> then `.alpha_(l).` doesn.t depend on temperature. <br/> Unit of `alpha_(l)` is `(""^(@)C)^(-1)` or `K^(-1)`. <br/> In equation (1), `Deltal=l_(2)-l_(1)` and `DeltaT=T_(2)-T_(1)`, <br/> `l_(2)=l_(1)=alpha_(l)l_(1)(T_(2)-T_(1))` <br/> `:.l_(2)=l_(1)+alpha_(l)l_(1)(T_(2)-T_(1))` <br/> `:.l_(2)=l_(1)[1+alpha_(l)(T_(2)-T_(1))]` <br/> By taking `alpha_(l)=alpha` and `l_(1)=l` <br/> `l_(2)=l[1+alpha(T_(2)-T_(1))]` <br/> <img src="https://doubtnut-static.s.llnwi.net/static/physics_images/KPK_AIO_PHY_XI_P2_C11_E01_010_S01.png" width="80%"/> <br/> In above table, special average values are given for some <a href="https://interviewquestions.tuteehub.com/tag/elements-969381" style="font-weight:bold;" target="_blank" title="Click to know more about ELEMENTS">ELEMENTS</a> for `0^(@)C` to `100^(@)C` temperature interval. <br/> From this table, if `alpha_(l)` for glass and <a href="https://interviewquestions.tuteehub.com/tag/copper-933790" style="font-weight:bold;" target="_blank" title="Click to know more about COPPER">COPPER</a> are compared, then it is seen that for the same increases in temperature, copper expands 5 times more than glass. <br/> In general, expansion is more in <a href="https://interviewquestions.tuteehub.com/tag/metals-1094891" style="font-weight:bold;" target="_blank" title="Click to know more about METALS">METALS</a> and their values of `alpha_(l)` are high.</body></html>


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