A 160 watt light source is radiating light of wavelength `6200 Å` uniformly in all directions. The photon flux at a distance of `1.8 m` is of the order of (Plank's constant `6.62 xx 10^(-34) J-s`)

Options

A. `10^(2) m^(-2)s^(-1)`
B. `10^(12) m^(-2)s^(-1)`
C. `10^(19) m^(-2) s^(-1)`
D. `10^(25) m^(-2) s^(-1)`

Answer

C

Explanation

`(N)/(4 pi R^(2))N=(160xx6200xx10^(-10))/(6.61 xx10^(-34) xx3 xx10^(8))`
`=(5xx10^(19)xx10)/(4 xx3.14 xx3.24)=(16xx62 xx10^(-7))/(20 xx10^(-34)xx10^(8))`
`=(5 xx 10^(19)xx10)/(4xx3.14xx3.24)=(496)/(10)xx10^(19)=1.25 xx 10^(19)`.