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 figure. Study the graph carefully and answer the following questions : (i) What do the horizontal regions AB and CD represent? (ii) if CD = 2AB, what do you infer ? (iii) The slope of OA gt the slope of BC. What does this indicate ? (iv) What does the slope DE represent ?

A solid material is supplied with heat at a constant rate. The tempera

1.	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 figure. Study the graph carefully and answer the following questions : (i) What do the horizontal regions AB and CD represent? (ii) if CD = 2AB, what do you infer ? (iii) The slope of OA gt the slope of BC. What does this indicate ? (iv) What does the slope DE represent ?
Answer» SOLUTION :(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")`