Pinhole Projection

Laptop smiley-face mask pointed toward a pinhole in cardboard

Hello girls! Today we're going to project a smiley face onto the wall--using two pieces of cardboard, and some white light.

You'll need:
Two pieces of thin cardboard (like from cereal boxes), each larger than the screen you're using
A screen, like from a laptop
Scissors
Darkness (a room with no windows, or another room at nighttime)

That's it!  An adult could probably be pretty helpful on this project.

First, you create your mask. The mask is something that blocks light you don't want, and lets through light in the shape you do want.  We do this by cutting a big smiley face out of a piece of cardboard (but don't make it bigger than your screen).  Light can get through the parts you cut out, but not through the cardboard.  Thus, it is a mask.

Next, we create our pinhole.  Make a hole just a little too small for a pencil to fit through.

The pinhole is the only place light can get past the cardboard.  Check out the diagram below.  Light only travels in straight lines.  This means that in the bottom part of the picture (the trunk of this tree), light only travels to the pinhole if it's going upwards.  At the top of the picture (the leaves of the tree), light only gets through the pinhole if it's headed downwards.  They don't change directions as they shoot through the pinhole--so the picture ends up upside down!  This is pretty tricky stuff, so don't worry if it doesn't make perfect sense right now.

Now, let's see our projection in action!  Face your screen towards a blank white wall, only a few feet away.  Cover it with your smiley face mask.  Make sure the screen is as bright as it gets, and that you can make the room really dark.  Now, put the big sheet of cardboard with the pinhole in the middle right between the screen and the wall, and turn off the lights.  Your smiley is projected on the wall!  And it's upside down, of course!  Just flip the mask upside down and the outline on the wall will be perfect.  My smiley is very shy and dim, so I could not get a picture--this is a project to enjoy in person!  It's really very cool--I hope you enjoy it as much as I did.