Unit 29
Seeing and sensing.
Waves, sound and light at work in a laser, a telescope, a camera, a CT scanner and a sonar.
Before this unit
The unit, lesson by lesson
Lessons
5 lessons · 33 practice questions · about 2 hours
Lasers
A ruby laser: photons of one energy, a threshold above which a beam appears, stimulated emission that copies photons, and a mirror that leaks too much.
Telescopes
A telescope does three things: it gathers light, separates detail and magnifies. The eyepiece sets the magnification, but only the aperture sets how much light and how much detail, because of diffraction.
Cameras and image sensors
A camera counts photons: the aperture and the shutter set how much light reaches each pixel, the ISO only amplifies what was counted, and few photons mean grain.
Medical imaging
A CT scanner measures how much X-ray light gets through the body from many directions, and rebuilds a slice from it. Why one reading is not enough, how many directions it takes, and why the lungs show black.
Sonar and echolocation
A sonar maps the seabed with echoes: depth from the echo's time, a beam whose width the wavelength sets, and a frequency that trades detail against range.