# Search results for query: *

• Users: Frodo
• In Optics
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1. ### What is the relationship between refraction and giant waves in Nazaré?

Normal sea waves close to the shore behave exactly like tsunami waves. Both a 'wind driven wave approaching the beach' and a 'tsunami wave during its entire journey' are shallow water waves meaning their wave length is longer than the water depth and their speed is proportional to the depth...
2. ### What is the relationship between refraction and giant waves in Nazaré?

The way in which the Nazerre wave is created is explained in https://www.surfertoday.com/surfing/the-mechanics-of-the-nazare-canyon-wave where the critical importance of the underwater canyon is discussed, as is how the sea floor profile causes the wave to refract. Other factors also contribute...
3. ### What causes this curious light phenomenon? (video inside)

It is almost certainly because the fan casing is rotating about a vertical axis causing the wires on the front to interact differently with the wires at the back depending on the angle. The back wires sometimes align side-by-side with the front wires, blocking 'two wire widths of light' and...
4. ### What causes this curious light phenomenon? (video inside)

You see the same Moiré fringe effect when driving and you approach a bridge with handrails held by vertical rods (say, 1 inch in diameter, 6 inches apart) crossing the road. The near side rods and the far side rods "bunch together" and you see horizontally moving bands of brightness and darkness.
5. ### Negative concave lens

Off topic, but you can distort a lens in a process known as lens bending where the lens keeps essentially the same characteristics.
6. ### Negative concave lens

Thank you for the clarification though I think you are off topic. The original post said "double convex" and "double concave" and asked "What exactly is a negative concave lens?" I was answering this limited case - what is a negative double concave lens? My answer is then correct. The...
7. ### Negative concave lens

The statement is a bit confusing as negative and concave effectively mean the same thing. A concave lens has a negative focal length so calling it a "negative concave" lens is somewhat tautological. A convex lens has a positive focal length. When you use the formula 1/u + 1/v = 1/f, f will be...