The sun gives light at the rate of `1400Wm^(-2)` of area perpendicular to the direction of light. Assume `lamda(sunlight)=6000A`. Calculate
A.the number of photons per second arriving at `1 m^2` area at earth.
B. the number of photons emitted from the sun per second assuming the average radius of the Earth's orbit is `1.49xx10^(11)` m.

Explanation

`I = 400 W//m^(2) , lamda = 6000 Å`
(a) Energy of the photon , `E = hupsilon =(hc)/lamda`
`(c = 3xx10^(8) m//sec)`
Let n be the number of photons received /sec per unit area.
`n=(IA)/(E_("Photon"))=((1400xx1)xx(6000xx10^(-10)))/(6.63 xx10^(-34)xx3xx10^8)`
`= 4.22 xx10^(21)`
(b) Total energy emitted per second = power (watt)
n/sec `=("Power of sun (W)")/("E/photon")`
`=(Ixx(4piR^2) xx(6000 xx 10^(-10)))/(6.63 xx 10^(-34) xx 3 xx 10^(8))`
(R is the average radius of earth.s orbit )
`= 1.178 xx 10^(45)`