A solid material is supplied with heat at a constant rate. The temperature of the material is changing with the heat input as shown in the graph in figure. Study the graph carefully and answer the following questions:

(i) What do the horizontal regions AB and CD represent?
(ii) If CD is equal to 2AB, what do you infer?
(iii) What does the slope of DE represents?
(iv) The slope of `OAgtthe` slope of `BC`. What does this indicate?

Explanation

(i) In the regions AB and CD the temperature of the material remains constant. So AB represents fusion and CD represents vapourisation.
(ii) CD= 2AB or `Q_(4) = 2Q_(2)`, it shows that latent heat of vapourisation is twice that of latent of fusion.
(iii) Let `S_(1) and S_(2)` be the specific heats of solid and liquid states respectively, then
`Q_(1) = mS_(1) Delta T_(1) " or " S_(1) = (1)/(m((Delta T_(1))/(Q_(1)) ) ) = (1)/( m xx "slope of OA")`
Similarly `S_(2) = (1)/(m xx "slope of BC")`
Since slope of OA `gt` slope of BC, `therefore S_(1) lt S_(2)`.
(iv) If `S_(3)` is the specifice heat of vapour state (region DE),
then `S_(2) = (1)/(m xx "slope of BC")`
or Slope of DE = `(1)/(mS_(3)) = (1)/("heat capacity")`