Question Number 47713 by ajfour last updated on 13/Nov/18
Commented by ajfour last updated on 13/Nov/18
$${If}\:{cylinder}\:{has}\:{length}\:{L},\:{find} \\ $$$${how}\:{much}\:{area}\:{of}\:{cylinder} \\ $$$${receives}\:{light}\:{from}\:{the}\:{point} \\ $$$${source}\:{at}\:{a}\:{distance}\:{d}\:{and}\:{at} \\ $$$${same}\:{level}\:{h}={R}\:{as}\:{its}\:{axis}. \\ $$$$\left(\:{instead}\:{of}\:{h}=\frac{{R}}{\mathrm{2}}\:{in}\:{diagram}\:\:\right). \\ $$
Commented by mr W last updated on 13/Nov/18
$${A}_{{lighted}} =\mathrm{2}\theta{RL}=\mathrm{2}{RL}\:\mathrm{cos}^{−\mathrm{1}} \frac{{R}}{{d}} \\ $$
Commented by mr W last updated on 14/Nov/18
Commented by ajfour last updated on 14/Nov/18
$${Thank}\:{you}\:{Sir},\:{i}\:{understood}\:{my} \\ $$$${poor}\:{recognition}! \\ $$