Light and Shadow Science for Grades 4–6: Umbra, Penumbra and Fair Tests
Light and Shadow Science for Grades 4–6: Umbra, Penumbra and Fair Tests
A flashlight, an opaque object, a screen and a ruler are enough to teach two big ideas: light travels in straight lines, and a fair test changes one thing at a time. Students measure shadows, draw boundary rays and use two lamps to find the partial shadow. The unit has a 12-page student book with six differentiated worksheets and a 7-page teacher guide.
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Light, Shadow & Penumbra | Shadow Size, Light Paths & Fair Tests | Physical Science Unit | Grades 4–6
Skills Starter Bundle | 10 Complete Units | ESL, Grammar, Science, Math, Music & German | Grades 2–12
Measurement, Data Analysis & Scientific Inquiry | Physics Unit | Grades 5–7
Drawing Activities | Light, Shadow & Shading Techniques | Middle School Art Unit | Grades 6–9
Light, Refraction & Lenses | Reflection, Snell's Law & Image Formation | Physics Unit | Grades 8–11
The teaching problem
Shadows are easy to make and hard to explain
Every child has made shadow puppets, so shadows feel familiar. Ask why a shadow grows when the flashlight moves closer, though, and the answers get vague. Some students think the shadow is something the object gives off. Others mix up size and darkness. Shadow work is also a good place to teach experimental method, and that chance often goes to waste. Students move the lamp, the object and the screen all at once, get a result, and have no idea what caused it. The fuzzy edge of a shadow, the penumbra, usually goes unexplained because it seems too advanced. It is not, if students count how many light sources can reach each spot. This topic needs measurement, a simple ray model and deliberate practice with controlling variables.
A sequence that works
How the investigation unfolds
Students measure before they model, and they check their method before taking the ideas outdoors.
- Make and describe a shadowStudents shine a flashlight on an opaque object and describe the shadow on the screen. The starting idea is simple: light travels in straight lines and the object blocks part of it.
- Change only the lamp distanceWith the object-to-screen distance fixed, students move the lamp and measure the shadow each time. Closer lamp, bigger shadow. Keeping one variable fixed is the lesson as much as the result.
- Draw boundary raysStudents sketch straight lines from the lamp past the edges of the object to the screen. The drawing becomes a model that predicts the shadow before anyone measures it.
- Add a second lampWith two flashlights, students count how many lamps reach each region. None means full shadow, one means partial shadow, both means fully lit. Umbra and penumbra now have a clear, testable meaning.
- Spot the flawed test, then go outsideStudents diagnose an experiment where two variables changed at once. Then they take the ray model outdoors and explain long and short shadows through the height of the Sun.
Where it goes wrong
Where students usually slip
The biggest methodological slip is changing two things at once, often without noticing. Before each measurement, have partners say aloud which distance is fixed and which one they are changing. On the science side, students often believe a darker shadow is a bigger one, or that the penumbra is some kind of reflection. The two-lamp worksheet addresses this, so give it enough time and let students test their predictions. Rooms that are not dark enough make edges hard to see; close the blinds or work in a corner. Repeat the safety rule the unit gives: never stare into bright light, and never look at the Sun, including during the outdoor task.
What's in the download
Inside the files
Print-ready PDF student book and teacher guide, with model answers throughout.
- 12-page student book with six worksheets
- Foundation, core and extension levels
- Knowledge page and image lab
- Extension tasks and a learning check
- 7-page teacher guide with model answers
- Differentiation and diagnosis notes
Good to know
Frequently asked questions
Is this aligned to the NGSS?
Shadow investigations usually sit in elementary physical science, and the fair-test tasks practice the NGSS science and engineering practice of planning and carrying out investigations. States place light topics at different grades, so check your own standards. TeachLessons is not affiliated with NGSS or Achieve, and this unit is not endorsed or approved by them or by any state.
What equipment do I need?
An LED flashlight, an opaque object, a screen or wall and a ruler for each group. A second flashlight is needed for the two-light-source worksheet. Phone flashlights can stand in if you are short, though a separate flashlight is easier for students to position and hold steady. A room you can darken helps the shadow edges show clearly.
Is it safe?
Yes, with the usual rule the unit repeats: do not stare into bright light and never look at the Sun. For the outdoor task, students look at shadows on the ground, not at the sky. Go over the rule before the first experiment and again before going outside, and keep flashlights pointed at the screen rather than at classmates.
Does it teach fair testing?
Yes, directly. Students change one variable, keep the others fixed and record their measurements. Later they diagnose an experiment where two variables changed at once and explain why its result cannot be trusted. The teacher guide includes model answers for these tasks, which makes it easier to give clear feedback on method and not only on the final number.
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Turn off the lights and measure
Download the unit, find a flashlight and a ruler, and let your class test how shadows really work.
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