Question

Suppose ${10}^{-17}$J of energy is needed by the interior of the human eye to see an object, how many photons of green light $(\lambda =550nm)$ are needed to generate this minimum amount of energy?

• A. 22
• B. 20
• C. 14
• D. 28

Answer 1

The correct option is D 28

According to Planck's quantum theory $E=\frac{nhc}{\lambda }$
Where, E = Energy of the radiation
n = number of photons per second
h = Planck's constant $=6.626\times {10}^{-34}Js$
c = speed of light =$3\times {10}^{8}m/s$
$\lambda$ = wavelength of the radiation $=550nm=550\times {10}^{-9}m$
So,
$E=\frac{n\times 6.626\times {10}^{-34}\times 3\times {10}^8}{550\times {10}^{-9}}$
$=\frac{{10}^{-17}}{3.61\times {10}^{-19}}=27.7\approx 28$

So, the number of photons required is 28.