# Homework Help: Rate of Photon Strike

1. Apr 11, 2005

### Jacob87411

Monochramatic light of wavelength 300 nm is incident normally on a surface of area 4 cm squared. If the intensity of the light is 15x10^-2 W/m^2, determine the rate at which photons strike the surface.

Honestly when reading this I thought I missed something in the chapter. A wave of 300nm strikes a metal surface that is 4 centimeters squared. The light intensity strikes with 15x10^-2. Im just lost on how to start it because I havent seen anything like it in this chapter.

2. Apr 11, 2005

### stunner5000pt

I = power/ area
power = energy / time
energy of each photon is given by hc/lambda
so the enrgy of a certain number,n of photons is nhc/lambda
im not quite sure how to eliminate the time in the equation you will get... perhaps someone else will helpm since i too am curious on how to solve something like this

3. Apr 11, 2005

### dextercioby

The rate of photons means #of photons each second.The # of photons can be computed by dividing the transfered energy to the surface by the energy of one photon...That "/s" is gotten by diving the power (energy in unit time) and not the energy.

$$\mbox{No.photons \ per \ s}=\frac{15\cdot 10^{-2} \ \frac{W}{m^{2}}\cdot 4\cdot 10^{-4}m^{2}}{\frac{hc}{\lambda}}$$

Daniel.

Last edited: Apr 11, 2005
4. Apr 11, 2005

### stunner5000pt

ok sorry i dont mean to hijack your thread but dexter can u take a look at my thread on index of refraction i nteh college level forum?

5. Apr 11, 2005

### Jacob87411

Thanks, that helps a lot..made it a lot clearer