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Question
If a = 0.72 and r = 0.24, then the value of tr is ______.
Options
0.02
0.04
0.4
0.2
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Solution
If a = 0.72 and r = 0.24, then the value of tr is 0.04.
Explanation:
Express the relation of absorptivity. The fraction of light/ray/radiation absorbed by a surface is called absorptivity.
`a = (G_(abs))/G`
`G_(abs) =Ga`
Here, `G_(abs)` is absorbed radiation and G is incident radiation.
Express the relation of reflectivity.
The fraction of light reflected by a surface is known as reflectivity.
`r = (G_(ref))/G`
`G_(ref) = Gr`
Here, `G_(ref)` is reflected radiation.
Express the relation of transmissivity. The fraction of light/ray/radiation transmitted by a surface is known as transmissivity.
`t_r = G_t/G`
`G_t = Gt_r`
Here, `G_t` is transmitted radiation.
Express the relation of 1st law of thermodynamics. Sum of all radiation (absorbed, reflected and transmitted) should be equals to the total radiation.
`G_(abs) + G_(ref) + G_t = G` ......(i)
Substitute `Ga` for `G_(abs), G_r` for `G_(mf)` and Gt for Gt in equation (i).
`(Ga)/G + (Gr)/G + (Gt_r)/G` = 1
`a + r + t_r` = 1
Substitute 0.72 for a and 0.24 for r to find transmitted radiation.
0.72 + 0.24 + tr = 1
tr = 1 – 0.96
tr = 0.04
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