Highly selective Backlog Qs for JEE MainPhysicsThermal Properties of Matter
Which of the following statements is true/correct?
Options
- ADuring clear nights, the temperature rises steadily upward near the ground level
- BNewton's law of cooling, an approximate form of Stefan's law, is valid only for natural convection
- CThe total energy emitted by a black body per unit time per unit area is proportional to the square of its temp
- DTwo spheres of the same material have radii 1 ~m and 4 ~m and temperatures 4000 ~K and 2000 ~K respectively. T
Correct answer
B. Newton's law of cooling, an approximate form of Stefan's law, is valid only for natural convection
Step-by-step solution
During clear nights object on surface of earth radiate out heat and temperature falls. Hence option (a) is wrong. The total energy radiated by a body per unit time per unit area E T⁴ . Hence option (c) is wrong. Energy radiated per second is given by aligned Q t &=P A T⁴ P₁ P₂ &= A₁ A₂ ( T₁ T₂ )⁴= ( r₂ )² ( T₁ T₂ )⁴ &= ( 1 4 )² ( 4000 200 )= 1 1 aligned P₁=P₂ , hence option (d) is wrong. Newton's law is an approximate from of Stefan's law of radiation and works well for natural convection. Hence option (b) is corre