Question

Eye can detect a signal (colour) of 900 nm, if
total energy of such photons exceeds 5.5 x 10-13 J.
How many minimum photons has to strike on eye to
detect signal? [Take, h = 6.6 x 10-34 Js]


the correct answer will be marked as brainliest​

Answer 1

Given that,

Wavelength detected by eye, $\lambda=900\ nm$

Total energy, $E=5.5\times 10^{-13}\ J$

To find,

Minimum number of photons has to strike on eye to  detect signal.

Solution,

Let there are n number of photons. Energy of n photons is given by :

$E=\dfrac{nhc}{\lambda}$

h is Planck's constant and c is speed of light

$n=\dfrac{E\lambda}{hc}\\\\n=\dfrac{5.5\times 10^{-13}\times 900\times 10^{-9}}{6.6\times 10^{-34}\times 3\times 10^8}\\\\n=25\times 10^5$

So, $25\times 10^5$ minimum photons has to strike on eye to detect signal.