Question

The graph, shown in the diagram, represents the variation of temperature (T) of the bodies, x and y having same surface area, with time (t) due to the emission of radiation. Find the correct relation between the emissivity and absorptivity power of the two bodies

• A. $E_x>E_{y}and{a}_x<a_y$
• B. $E_x<E_{y}and{a}_x>a_y$
• C. $E_x>E_{y}and{a}_x>a_y$
• D. $E_x<E_{y}and{a}_x<a_y$

Answer 1

The correct option is C $E_x>E_{y}and{a}_x>a_y$

Rate of cooling $(-\frac{dT}{dt})\infty$ emissivity (e)
From the graph,
${(-\frac{dT}{dt})}_x>{(-\frac{dT}{dt})}_y$
$\therefore E_x>E_y$
Further emissivity (E) = absorptive power (a) (good absorbers are good emitters also)
$\therefore a_x>a_y$