The graph signifies:

Two substances $A$ and $B$ of equal mass are heated at a constant rate of $6 \ cal \ s^{-1}$. The graph shows the temperature versus time. What is the ratio of the heat absorbed for complete melting $H_A/H_B$?

$A$ solid cube having certain fixed melting and boiling points takes heat from some source. The variation of temperature $\theta$ of the cube with the heat supplied $Q$ is shown in the adjoining graph. The portion $BC$ of the graph represents the conversion of

$A$ solid substance is at $30^{\circ}C$. To this substance,heat energy is supplied at a constant rate. The temperature versus time graph is as shown in the figure. The substance is in the liquid state for the portion of the graph:

$A$ solid material is supplied with heat at a constant rate. The temperature of the material changes with heat input as shown in the figure. What does the slope of $DE$ represent?

Explain the process of change in the state of matter by heating or cooling it.