Q.
Suppose 10−17J of light energy is needed by the interior of the human eye to see an object. How many photons of green light (λ=550nm) are needed to generate this minimum amount of energy?
The energy needed to see object =10−17J
Photon energy used to see object =λhc =550×10−96.626×10−34×3.0×108 =3.61×10−19J/ photon ∴ Number of photons =3.61×10−1910−17=27.7 ∴ Minimum number of photons required to see object =28.