Question

If ${10}^{-17}$ J of light energy is needed by the interior of the human eye to see an object. The photons of green light needed to see the object are:

$[\lambda =550nm]$

• A. $27$
• B. $28$
• C. $29$
• D. $30$

Answer 1

Answer: (B)

$28$

Required energy $={10}^{-17}J=n\times \frac{hc}{\lambda }$

$\Rightarrow n\times \frac{6.625\times {10}^{-34}\times 3\times {10}^8}{550\times {10}^{-9}}J={10}^{-17}J$

$\therefore n=27.65\approx 28$.

Hence, the correct option is $B$