Physics-
General
Easy

Question

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

  1. e subscript x end subscript greater than e subscript y end subscript & a subscript x end subscript less than a subscript y end subscript    
  2. e subscript x end subscript less than e subscript y end subscript & a subscript x end subscript greater than a subscript y end subscript    
  3. e subscript x end subscript greater than e subscript y end subscript & a subscript x end subscript greater than a subscript y end subscript    
  4. e subscript x end subscript less than e subscript y end subscript & a subscript x end subscript less than a subscript y end subscript    

The correct answer is: e subscript x end subscript greater than e subscript y end subscript & a subscript x end subscript greater than a subscript y end subscript


    Rate of cooling open parentheses negative fraction numerator d T over denominator d t end fraction close parentheses   proportional to emissivity (e)
    From graph, open parentheses negative fraction numerator d T over denominator d t end fraction close parentheses subscript x end subscript greater than open parentheses negative fraction numerator d T over denominator d t end fraction close parentheses subscript y end subscript Þ e subscript x end subscript greater than e subscript y end subscript
    Further emissivity (e) µ Absorptive power (a) Þa subscript x end subscript greater than a subscript y end subscript
    (becausegood absorbers are good emitters).

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