p19_018.pdf

18. The change in length for the section of the steel ruler between its 20 . 05 cm mark and 20 . 11 cm mark is

∆ L s = L s α s ∆ T =(20 . 11 cm)(11

10 − 6 / C ◦ )(270 ◦ C

−

20 ◦ C) = 0 . 055 cm .

20 . 05 cm)+0 . 055 cm = 0 . 115 cm. The

coe#cient of thermal expansion for the material of which the rod is made of is then

−

α = ∆ L

0 . 115 cm

270 ◦ C

−

20 ◦ C =23

10 − 6 / C ◦ .

Thus, the actual change in length for the rod is ∆ L =(20 . 11 cm

∆ T =