An optical illusion is an image that deceives the eye by appearing to be something other than what it is. The image can use color, light, and patterns to trick our brains into trying to make sense out of what we see, even if what we see isn't real. And since kids love tricky things, they tend to love optical illusions.
The website Optics4Kids is all about optics and optical illusions. You can find tons of illusions on the site that pose questions for your kids to try and figure out. The answers are listed in case something is a little too hard.
Here's an example:
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Optics4Kids also offers a bunch of hands-on DIY activities to help kids understand the physics of light. There are activities for ages 5 and up, ages 10 and up, and ages 15 and up. Kids will be able to do things like create a water prism to break light into the seven colors of the rainbow, make a lens and see how their eyes manipulate the light that enters it, and use Jell-O to explore lenses and different angles of light entry.
Check out all the activities here.