Question

Distinguish between isobar and isotherm.

Answer 1

Isobars and isotherms are lines or contours on a map that join points having the same pressure and temperature respectively. Isobars and isotherms have varied purposes especially in the fields of thermodynamics and geography.

Complete answer:

Isobar	Isotherm

1. It is the contour or line joining the points on a map or a thermodynamic plot of an ideal gas for which the pressure remains constant.| 1) It is the contour or line joining the points on a map or a thermodynamic plot of an ideal gas for which the temperature remains constant.
2. In geographical terms, an isobar will be the curve joining the locations on a map where the pressure is the same.| 2) In geographical terms, an isotherm will be the curve joining the locations on a map where the temperature is the same.
3. In thermodynamics, an isobar is obtained when the gas undergoes an isobaric process (its pressure remains constant throughout).| 3) In thermodynamics, an isotherm is obtained when the gas undergoes an isothermal process (its temperature remains constant throughout)
4. The internal energy of an ideal gas can change when going on an isobar. | 4) The internal energy of an ideal gas remains constant when going on an isotherm.

Note:
Students must note that in the field of thermodynamics there is another curve called the isochore. This is the line or contour joining all the points on a thermodynamic plot between a gas’s pressure and temperature where the volume of the gas remains constant, that is, while travelling on this curve, the gas neither expands or contracts. In a sense, it can also be said that on the isochore, the gas does not do any mechanical work.