Question

Assume that $2\times {10}^{-17}$ J of light energy is needed by the interior of the human eye to see an object. How many photons of yellow light with λ=595.2 nm are needed to generate this minimum energy?

• A. 6
• B. 30
• C. 45
• D. 60

Answer 1

The correct option is D 60

Enegy of a photon$=hc/\lambda$
Enegy of n number of photons $=nhc/\lambda$
$E=\frac{nhc}{\lambda }$
By substituting:
$E=2\times {10}^{-17}J$
$h=6.62\times {10}^{-34}J$
$c=3\times {10}^{8}m{s}^{-1}$
$\lambda =595.2\times {10}^{-9}$
we get $n=60$