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Method 1: Water Glass Rainbow
You do not need an expensive prism to make a rainbow! A glass of water works too.
Fill a clear glass with water and place it on a windowsill where sunlight shines through it. Hold a white piece of paper next to the glass and move it around until you see a rainbow on the paper!
The water in the glass acts like a prism. When sunlight passes through the curved glass and water, it bends and splits into colors. You might see the rainbow projected on the wall, the floor, or your paper.
Tip: a round glass works better than a square one because the curved surface bends light more effectively.