Chapter 27, Problem 18P

To determine

Number of photons lead to an observable flash.

Answer to Problem 18P

Solution:

Number of photons lead to an observable flash is $3$.

Explanation of Solution

Given:

Work function, $E={10}^{-18}\text{J}$

Wavelength of visual sensitivity, $\lambda =550\text{nm}=\text{550}\times {\text{10}}^{-9}\text{m}$

Formula used:

The number of photons is calculated as

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

Here,

$n$ is number of photon

$h=6.62\times {10}^{-34}\text{J-s}$ is the Planck’s constant

$c=3\times {10}^8\text{m/s}$ is the speed of light

$\lambda$ is the wavelength

Calculation:

The number of photons is calculated as

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

Plugging the values in the above equation

$\begin{array}{c}{10}^{-18}=\frac{n\times 6.62\times {10}^{-34}\times 3\times {10}^8}{550\times {10}^{-9}}\\ n=2.7\\ \approx 3\end{array}$