Counting Photons
Part of the Optics, Waves and Modern Physics section of Coddy's Physics journey. Lesson 38 of 53.
Photons per second:
N = Pλ / hc
A 1 mW red laser: about 3 × 10¹⁵ photons a second.
One electron per photon: the current is I = N e.
Challenge
A red laser pointer gives out 1 mW of light of wavelength 650 nm. How many photons N does it send out each second?
Try it yourself
Test yourselfThis lesson includes a short quiz. Start the lesson to answer it and track your progress.
All lessons in Optics, Waves and Modern Physics
1Reflection and Refraction
Reflection of LightThe Refractive IndexSnell's LawTotal Internal ReflectionDispersionApparent DepthRecap - Optical Fiber4Mechanical Waves
What a Wave IsTwo Graphs of a WaveWhen Pulses MeetInterferenceStanding WavesHarmonicsRecap - Guitar String