Question

the energy per photon of a red laser (wavelength = 642 nm) is 3.1 × 10^{-19} j. how many photons are in a 25 j pulse of laser light?
______ photons
report your answer with two significant figures. do not include units in your answer. report your answer in scientific notation with the format 2.2e2 or 2.2e - 2.

Explanation:

Step1: Determine the formula

The number of photons \(n=\frac{\text{Total energy}}{\text{Energy per photon}}\)

Step2: Substitute the values

Given total energy \(E_{total} = 25\space J\) and energy per photon \(E_{photon}=3.1\times 10^{-19}\space J\)
\(n=\frac{25}{3.1\times 10^{-19}}\)

Step3: Calculate the value

\(n=\frac{25}{3.1}\times10^{19}\approx 8.0645\times 10^{19}\)
Rounding to two significant figures, \(n = 8.1\times 10^{19}\)

Answer:

8.1E19