Physics educators have used photos of natural and man-made breakwaters to show refraction for probably as long as we’ve had photography. But now online mapping web sites (Google, Yahoo. etc.) allow you to find locations near you to make the images more tangible to your students. Oceans and bays are full of images of refraction, but you may also find diffraction patterns in a large lake.
Below is an example from a breakwater in Berkeley, CA, in the San Francisco Bay
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Check water bodies around your institution to find examples you can use with your students. Most mapping sites allow you to save landmarks in a “My maps” section, so once you find a good location, you can save it, then pull it up from a list when you need to show it in class.
One warning: Map sites update their satellite photographs every so often (as the USGS releases newer ones), so check your location before your lecture to make sure your pattern is still there!