Total internal reflections occur when light traveling through a medium reaches a boundary with a lower refractive index and is completely reflected back into the medium.

Complete internal reflections can be observed in certain optical systems.

Total internal reflexions occur when light traveling through a medium reaches a boundary with a lower refractive index and is completely reflected back into the medium.

Total internal reflexion is a phenomenon that occurs when light traveling in a medium with a higher refractive index is reflected back into the same medium instead of being transmitted into a medium with a lower refractive index.

After years of unemployment, he finally found a job and was brought in from the cold.

We all agreed in one voice to support the new proposal.

They are mucking in to help clean up the park.

He mucks in and helps with the cleaning.

He always carries pills in his pocket.

They mucked in to help clean up the park.