A star which can be seen with naked eye fro Earth has intensity `1.6xx10^(-9)Wm^(-2)` on Earth.If the corresponding wavelength is 560 nm,and the radius of the lens of human eye is `2.5xx10^(-3)`m,the number of photons entering in our eye in 1s is…….

Explanation

`I=1.6x10^(-9)(W)/(m^(2))`
`lambda=560 nm=5.6xx10^(-7)m`
`r=2.5xx10^(-3)m`
t=1s,n=?
`I=(E )/(At)=(P)/(A)`
`therefore P=IA=I(pir^(2))` If number of photons entering in eye are n,its energy E=power (P)
`therefore P=(nhc)/(lambda)`
`therefore n=(plambda)/(hc)`
`=(3.14xx10^(-15)xx5.6xx10^(-7))/(6.62xx10^(-34)xx3xx10^(8))`
`therefore n=8.85xx10^(4)~~9xx10^(4)`