The expression for energy of photons is given by, E=
hc
λ
⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅(I) Substitute the values. E=
6.6×10−34×3×108
660nm
=3×10−19 The area of exposure of lamp at radius of 10m is calculated as A=4πr2 =4π×102m2 The area of sensor is given by, A′s=πr2 =π×(10−2)2 =π×10−4m2 The area of sensor is given by, A′s=πr2 =π×(10−2)2 =π×10−4m2 Thus, the energy emitted by lamp in exposure time is given by, E0=Poweroflamp(p)× exposure time (t) E0=300×100×10−3 =3J The expression for the number of photons is given by, N=