Question

The eyes of a certain member of the reptile family pass a visual signal to the brain when the visual receptors are struck by photons of wavelength $850\text{nm}$. If a total energy of $3.15\times {10}^{–14}\text{J}$ isrequired to trip the signal, the minimum number of photons that must strike the receptor is $x\times {10}^5$photons, find $x$. $(h=6.6\times {10}^{–34}\text{J s})$. Report the value upto two decimal.

Answer 1

We know that, $\text{Total energy}=n\times \text{Energy of one photon}$
$\text{Energy of one photon}=\frac{hc}{\lambda }$

$\therefore 3.15\times {10}^{–14}\text{J}=n\times \frac{(6.6\times {10}^{–34}\text{J s})(3\times {10}^8\text{m/s})}{850\times {10}^{–9}\text{m}}$

$\Rightarrow n=1.35\times {10}^5$