How many photons are produced in a laser pulse of 0.338 J at 505 nm?
1 Answer
Explanation:
You can start by figuring out the energy of a single photon of wavelength
To do that, use the equation
#E = h * c/(lamda)#
Here
#h# is Planck's constant, equal to#6.626 * 10^(-34)color(white)(.)"J s"# #c# is the speed of light in a vacuum, usually given as#3 * 10^8color(white)(.)"m s"^(-1)# #lamda# is the wavelength of the photon, expressed in meters
Plug in your value to find--notice that the wavelength of the photon must be expressed in meters in order for it to work here.
#E = 6.626 * 10^(-34)quad "J" color(red)(cancel(color(black)("s"))) * (3 * 10^8 color(red)(cancel(color(black)("m"))) color(red)(cancel(color(black)("s"^(-1)))))/(505 * 10^(-9)color(red)(cancel(color(black)("m"))))#
#E = 3.936 * 10^(-19) quad "J"#
So, you know that one photon of this wavelength has an energy of
#0.338 color(red)(cancel(color(black)("J"))) * "1 photon"/(3.936 * 10^(-19) color(red)(cancel(color(black)("J")))) = color(darkgreen)(ul(color(black)(8.59 * 10^(17) quad "photons")))#
The answer is rounded to three sig figs.