Bending Light
Interactive simulation of refraction and total internal reflection
Description
You can recite Snell's law and still be stuck on "at what angle does total internal reflection begin" when there is no picture in your head to go with the formula. This PhET simulation hands you the laser: drag its angle and the refracted beam swings in real time until, past a certain angle, the refracted ray vanishes and everything reflects back into the water — the critical angle stops being a number to memorize and becomes the moment you watched it happen.
The index of refraction on both sides is adjustable, with presets for air, water and glass and sliders for anything in between. Change one side and the refraction angle responds immediately, which is Snell's law made visible. Beyond the intro screen there is a Prisms mode for dispersion of white light and ray paths through differently shaped prisms, and a More Tools mode with a protractor, intensity meter and wave view for measuring how energy divides between reflection and transmission.
Light can be shown as rays or as waves, the latter making the change of wavelength between media visible. From PhET Interactive Simulations at the University of Colorado Boulder — free, HTML5, and usable offline.
Draggable laser: set the angle of incidence by dragging, with the refracted and reflected rays tracking the change so the relationship is watched rather than derived.
Total internal reflection: push past the critical angle and the refracted ray disappears as all the light returns to the original medium, showing the threshold directly.
Adjustable indices: the refractive index of each medium is set independently with air, water and glass presets plus continuous values, which makes verifying Snell's law straightforward.
Prisms mode: several prism shapes are available for observing white light dispersing into a spectrum and tracing paths through triangular and circular prisms.
Ray and wave views: light can be drawn as rays for path clarity or as waves to see wavelength compress and stretch across a boundary.
Measurement tools: the advanced screen adds a protractor, intensity meter and wave detector for measuring angles and the split of intensity between reflection and transmission.
Runs in a browser: HTML5 with no plugin, working on desktop and tablet browsers.
Offline capable: downloadable as a single HTML file for use without a connection.
Free and localized: free for teaching and self-study with many interface languages.
The index of refraction on both sides is adjustable, with presets for air, water and glass and sliders for anything in between. Change one side and the refraction angle responds immediately, which is Snell's law made visible. Beyond the intro screen there is a Prisms mode for dispersion of white light and ray paths through differently shaped prisms, and a More Tools mode with a protractor, intensity meter and wave view for measuring how energy divides between reflection and transmission.
Light can be shown as rays or as waves, the latter making the change of wavelength between media visible. From PhET Interactive Simulations at the University of Colorado Boulder — free, HTML5, and usable offline.
Features
Draggable laser: set the angle of incidence by dragging, with the refracted and reflected rays tracking the change so the relationship is watched rather than derived.
Total internal reflection: push past the critical angle and the refracted ray disappears as all the light returns to the original medium, showing the threshold directly.
Adjustable indices: the refractive index of each medium is set independently with air, water and glass presets plus continuous values, which makes verifying Snell's law straightforward.
Prisms mode: several prism shapes are available for observing white light dispersing into a spectrum and tracing paths through triangular and circular prisms.
Ray and wave views: light can be drawn as rays for path clarity or as waves to see wavelength compress and stretch across a boundary.
Measurement tools: the advanced screen adds a protractor, intensity meter and wave detector for measuring angles and the split of intensity between reflection and transmission.
Runs in a browser: HTML5 with no plugin, working on desktop and tablet browsers.
Offline capable: downloadable as a single HTML file for use without a connection.
Free and localized: free for teaching and self-study with many interface languages.
