Question

It is hotter at some distance over the flames then in front of it because:
(a) Air conducts heat upwards only
(b) Heat is radiated upwards only
(c) Convection of heat occurs upwards only
(d) Heat is radiated downwards only

Answer 1

At point in front of the flame heat occurs only due to radiation mode only while at some distance over the flames heat occurs due to both modes radiation as well convection that’s why it is hotter at some distance over the flames then in front of it.

Complete step by step answer:
There are three types of heat transfer conduction ,convection and radiation in conduction heat is transferred due to some medium in contact between the point where heat is transferred in convection there is a shift of molecules from one part of the medium to the other part of the medium due to some physical properties (mostly due to density difference) heat is carried by those molecules while in radiation no contact is required to transfer the heat in this process heat is transferred by electromagnetic radiations
In flames heat is transferred by two modes convection and radiation by radiation heat is transferred in all directions while by convection heat is transferred only in upwards direction that’s why it is hotter at some distance over the flames then in front of it.

Hence option (C) is correct.

Note: in flames it is hotter at some distance over the flames then in front of it because at front heat is due to radiation only no convection occurs in front of the flame while at some distance over the flame heat is due to both radiation and convection and convection occurs in upwards directions only.