Skip to Content Go to sign in Skip to Primary Navigation Skip to Secondary Navigation Skip to Page Navigation Skip to Header Navigation Skip to Footer Navigation Read more about accessability options and our navigation

Physics Classroom is making strides to make our site accessible to everyone. Our site contains 6 navigation areas. The Primary, Secondary, and Page Level navigations have a screen reader version of their nav structure that allows using the left and right keys to navigate sibling navigation items, and up or down keys to navigate parent or child navigation items. The others can be navigated using tabs. The Primary Navigation handles the first 2 levels of site pages. The Secondary (which is not always available) handles the 3rd and 4th level of structure. The Page level navigation allows you to navigate the current page's headings quickly. The Header Navigation contains the Light/Dark Mode toggle, Search, Notifications and account login. The Breadcrumb Navigation contains the breadcrumb of the current page. If the current page has a breadcrumb, you can get to it by skipping to the content and tabbing in reverse (shift plus tab). The Footer Navigation contains links such as Privacy, Contact, about and terms. Some resources contain an Audio Player that can be activated by holding down the T key for 3 seconds, and then using K to pause and resume. While not every area of Physics Classroom is usable purely from keyboard and screen reader, we are committed to continue work on making this possible. If you have questions or need additional help, please use this link to contact us.

Return to screen reader navigation
Home Interactives Refraction and Lenses Least Time Principle

Least Time Principle

The Least Time Principle Interactive is based on the classical premise that light always follows the pathway between two locations that takes the least amount of time. This Interactive uses the analogy of a lifeguard moving from the observation platform along sand, across the boundary into water, and through the water to reach a drowning swimmer. Of course, the path of least time is incredibly important. Learners will test several entry points to determine the entry point that results in the path of least time. Once they have done so, angles of incidence and refraction can be measured and analyzed.
🚀︎ Launch Interactive

Users are encouraged to open the Interactive and explore. For a more guided experience, The Physics Classroom has prepared an activity for use with this Interactive and encourages teachers to use it with their classes.

Learners and Instructors may also be interested in viewing the accompanying Notes page. Technical information, teaching suggestions, and related resources that complement this Interactive are provided on the Notes page. View Notes.

NEWOur Least Time Principle simulation is now equipped with Task Tracker functionality. Learn more.