## Refraction and Lenses

Refraction
Turn on your laser and shine it through air at the surface of water. Change the laser's angle and observe the effect. Swap out the water and replace it with oil or glass or diamond or ... . Switch to the other side of the boundary and observe the effect of laser light traveling from water to air. There's no end to what you can try with this Interactive ... without an expensive laser, without getting wet, and without having to buy any diamonds.

Least Time Principle
If you were a lifeguard at the beach and you saw a struggling swimmer in the water, it would be your objective to reach the swimmer in the least amount of time. But since you can run faster on the sand than you can swim in the water, you can't run directly at the swimmer. You can reduce your time by running a longer distance on the sand and swimming a shorter distance in the water. Your path to the swimmer will be a bent path - bent at the point where you transition from running to swimming. In this Interactive, learners will determine the entry point into the water that results in the least time. Then their analysis of the data will relate principle of least time to Snell's law of refraction. Now go save that swimmer ... in the least amount of time.

Optics Bench - Lenses
Every child has had the fascinating experience of looking through a magnifying glass. Many of us have taken the magnifying glass and looked at far away objects only to notice that the magnifying effect no longer occurs. So what exactly is going on with the lens of a magnifying glass? In this Interactive, learners will explore a converging lens. A candle can be dragged to varying locations and the characteristics of the image can be quickly observed. There is an activity sheet to accompany this Interactive.

The Physics Classroom thank their friends at Nerd Island Studios for contributing this Interactive to our collection.