PINHOLE INVESTIGATIONS

 Inquiry Starting Point -- Tabletop Light Source Activity

©1998 Exploratorium

Most people know very little about what happens when light comes through a pinhole. This activity provides an opportunity for teachers to experiment with pinholes and see how they work. This early stage of inquiry, sometimes called the "messing about", or exploratory stage, is what we are calling an inquiry starting point. Pinholes are an easily accessible, common phenomenon, and are a good starting point for inquiry because they create dramatically visible effects. They thus provide teachers with many opportunities to raise questions and begin to piece together their observations and understandings.

Time
40 - 60 minutes

Grouping
Groups of 2 to 4

Materials
(for 24 to 32 people)

  • butcher paper to cover tables
  • 6 Tabletop Light Sources, each with four windows
  • 6 light bulbs, each with a different filament (purchased at any hardware store)
  • 16 pushpins or "T-pins" (these make larger, more useful holes than regular straight pins)
  • about 48 pieces of black construction paper or aluminum foil, 4" x 5"

    It's easier to make a "clean" hole in the aluminum foil, but then it tends to tear more easily than construction paper. Use what works best for you.

  • masking tape
  • 16 screens made of cardboard, tagboard or white construction paper, at least 8 x 16 and folded in half so as to be able to stand up

 

Preparation

The darker you can make the room, the better it will be for observations. Set up each light source with (1) a bulb with a different filament in each one, and (2) a piece of black construction paper or aluminum foil over each of the four openings.

 

To Do and Notice

Introduce the activity by telling teachers that in their exploratory investigation of pinholes they are free to go in whatever direction they like. Start them working by asking them what they think they'll see if they make a hole in the black paper covering the Tabletop Light Source openings. Have them make one pinhole, then another. Are they surprised by the shape of the light coming through?

When teachers express surprise, suggest that they make more holes and maneuver the screen or revise the size of the hole to find out more information. After a while, have them walk around and look at the patterns on the other tables. Sometimes it takes about 20 minutes to adapt to the dark and really see what is happening.

 

Discussion

Ask teachers why they think the light patterns are different at each table. There may be several reasons offered-with children there often are. If so, each hypothesis can be used as the basis for a short investigation.

Ask them if the patterns are the same from all four windows of the Tabletop Light Source? What if they turn their light fixture at the top of the box?

To promote further inquiry, you can pose these questions:

  • what if you change the shape of the pinhole?
  • are some images more fuzzy than others?
  • can the image be made bigger or smaller?
  • can the image be turned right-side up?
  • what are the images we see other than the filament?

 

What's Going On

The light patterns on the table and the screen are images of the filament in the bulb, and therefore are different for each of the different bulbs you selected.

Patterns on different sides of the same light source may be different because the image coming through the pinhole at each window is of the filament from a different orientation. A "c" shaped filament can have a "c", or an "I" image projected through the pinholes.

If you replace the clear bulb with a soft frosted bulb, teachers will see an image of the whole light fixture and understand that the image is upside down.

For a more detailed explanation, see Pinhole Images-What's Happening Here?