Pumpkin Lab: Light Through a Pumpkin

Before you start: try it once yourself

Turn the lights off on the starter pumpkin and look at the wall yourself once before you start, about ten minutes.

1. Open the lesson. Go to mytekdev.com/try/pumpkinlab?lesson=light-through-a-pumpkin&ref=fam-pumpkin-1. Click Carve: the four cuts are 1. Triangle cut through, 2. Triangle shaved, 3. Triangle cut through, 4. Grin painted. The readout under the stage says 2 cut through, 1 shaved.
2. Lights off. Press Night over the stage. The left eye and the nose blaze, the right eye glows dimmer, the grin stays dark.
3. The wall. Press Back in the row of view buttons. The cut eye's light lands on the far wall, bigger than the eye.
4. Change a mark. Tap 4. Grin in Your cuts and press Cut through. At night it now blazes too.
5. Grow an eye. Tap 1. Triangle and move Size. The patch on the wall grows with it.

Three ways to carve, at night.

The Back view: the cut eye's light on the far wall.

The ideas, in plain words

When light meets a material, it can be transmitted (it passes through), absorbed (it is taken in and goes no further) or reflected. A pumpkin's skin and thick flesh absorb almost all of a candle's light, so a jack-o'-lantern is dark except where it is carved. A hole transmits the light completely. A shaved patch, where only the skin is peeled off, leaves a thin layer of flesh: some light gets through, scattered in every direction, so it glows without showing a clear shape. That in-between material is called translucent; the thick, unshaved skin is opaque.

Light from a small source travels in straight lines. The rays that get through a hole keep going in straight lines and spread apart as they travel, so the patch of light they make on a far wall is the shape of the hole, only bigger. The farther the wall, the bigger the patch. That is the same geometry as a shadow cast by a small light. The scattered light from a shaved patch does not travel on as a beam, so it makes no shape on the wall.

In the lab, Night turns the room dark around the pumpkin and lights the candle inside it; the room has walls that catch the light that leaves each cut. The Back view looks past the pumpkin at the wall the face shines on.

Do it together

1. Open mytekdev.com/try/pumpkinlab?lesson=light-through-a-pumpkin&ref=fam-pumpkin-1 together. A short guide runs along the bottom; follow it. Click Carve at the top and read the four cuts under Your cuts.

   You'll know it worked when: 1. Triangle cut through, 2. Triangle shaved, 3. Triangle cut through, 4. Grin painted.

2. Before turning the lights off, your child predicts what each mark will do in the dark: glow brightly, glow a little, or stay dark.

   If you get stuck: Cut through is a hole. Shave the skin peels the skin off and leaves the flesh. Paint only is a drawing on the skin.

3. Press Night, over the pumpkin. Compare with the predictions.

   You'll know it worked when: The two holes blaze, the shaved eye glows a duller orange, and the painted grin stays dark.

4. Press Back, in the row of view buttons, to look past the pumpkin at the wall.

   You'll know it worked when: A bright shape lands on the wall from the cut-through eye, much bigger than the eye. The shaved eye throws nothing.

5. Change one thing: tap 4. Grin under Your cuts, press Cut through, and look again at night.

   You'll know it worked when: Now the grin blazes too.

6. Tap the left eye and move its Size slider at night, watching the wall. Then draw it on paper: a dot for the candle, a gap for the eye, a line for the wall, and straight lines from the dot through the edges of the gap.

   If you get stuck: The lines spread apart as they go, so they hit the wall farther apart than the edges of the eye.

7. Finish with one question: why does the shaved eye glow but throw nothing on the wall?

   You'll know it worked when: Your child explains that light gets through the thin flesh but spreads out every way, so only a hole sends straight rays in the eye's shape.

Talk about it

Ask these while you work together. A child who has understood the lesson can answer them without help:

• Which marks transmit the light, and which absorb it?
• Why does the shaved eye glow but throw no shape on the wall?
• What did you change in your test, and what did you keep the same?
• What happens to the patch on the wall when the eye gets bigger?
• Draw one ray from the candle through the top of the eye to the wall.

Bring it into other subjects

• Math: measure the eye and its patch on the wall in two sizes. Is the patch always the same number of times bigger?
• Art: design a face that uses all three kinds of mark, so it reads two ways: by day and at night.
• History: find out what people carved before pumpkins (turnips in Ireland and Scotland). The lab has a turnip under Style.
• Engineering: on the Light bench, try the Tea light and the Light bulb. Which would you choose for a real pumpkin, and why?

Quick check

Name: ______________________________

1. Which mark throws its shape onto the wall at night? (A) painted, (B) shaved, (C) cut through.

2. A shaved eye at night: (A) glows, but throws no shape on the wall, (B) stays dark, (C) throws a bigger shape than a hole.

3. Why is the face on the wall bigger than the face on the pumpkin?

Answers

Seen in the lab: at Night the cut-through left eye and nose shine brightly and the cut eye throws a bright patch on the far wall (Back view), the shaved right eye glows dimmer and throws nothing, and the painted grin stays dark. Changed to Cut through, the grin shines too.