PHYSICS - OBJECTIVE 2

2.Liquid oxygen at 50k is heated to 300k at constant pressure of 1 atm. The rate of heating is constant Which of the following graphs represents the variation of temperature with time ?

Answer : (c)

Answer explanation :This is related to heat transfer which are classified as conduction Convection and radiation . Isobaric process is constant pressure at varying temperature 

Now the graph depicting temperature with time is depicted as follows 

first line is positive gradient line, which is linear; second line is horizontal with no change in temperature; third line is parabolic curve which is exponential .This can be explained as follows

 The first curve has to be positive gradient line because liquid oxygen takes heat and becomes gas in three steps as shown below 

 

This is because linearity in conduction is positive gradient slope for heavy metals like oxygen.

 Next is convection , linearity is horizontal. Next is radiation, which is exponentially parabolic due to entropy. 

Now where is conduction here?  Here first line is isentropic; second line is isothermal and third line is isobaric in nature, why because liquid oxygen condenses into solid at constant heat initially, so conduction is involved. This is followed by Convection which is linear for heavy metals like oxygen and hydrogen (for example, boiling of water due to constant fire heat)

 Next comes radiation which is entropy based process molecules (liquid) separate from each other and becomes gas at wider intermolecular space ratio and the above graph is correct