Heat Transfer Set 2

hr (time) ✘ sqm (area) ✘ cm (thickness) ✔ kcal (heat). ✔

directly proportional to the surface area of the body ✘ directly proportional to the temperature difference on the two faces of the body ✘ dependent upon the material of the body ✘ inversely proportional to the thickness of the body ✔ all of the above. ✔

glass ✘ water ✘ plastic ✘ rubber ✔ air. ✔

steam ✘ solid ice ✘ melting ice ✘ water ✔ boiling water. ✔

composition ✘ density ✘ porosity ✘ structure ✔ all of the above. ✔

quantity of heat flowing in one second through one cm cube of material when opposite faces ^re maintained at a temperature difference of 1 ✘ quantity of heat flowing in one second through a slab of the material of area one cm square, thickness 1 cm when its faces differ in temperature by 1 ✘ heat conducted in unit time across unit area through unit thickness when a temperature difference of unity is maintained between opposite faces ✘ all of the above ✔ none of the above. ✔

aluminium ✘ steel ✘ brass ✘ copper ✔ lead. ✔

high thickness of insulation ✘ high vapour pressure ✘ less thermal conductivity insulator ✘ a vapour seal ✔ all of the above. ✔

electric heater ✘ steam condenser ✘ melting of ice ✘ refrigerator condenser coils ✔ boiler. ✔

it is impossible to transfer heat from low temperature source to t high temperature source ✘ heat transfer by radiation requires no medium ✘ all bodies above absolute zero emit radiation ✘ heat transfer in most of the cases takes place by combination of conduction, convection and radiation ✔ rate of heat transfer depends on thermal conductivity and temperature difference. ✔