Measure the Width of Human Hair Science Lesson Plan

Project Description

In this science lesson plan, lasers are used for measuring the tiniest things – like the width of a human hair! This hands on lesson brings STEM to light! Students will determine width of human hair using diffraction and a LASER Blox of known wavelength.

Grades: 9 to 14
Duration: 1/2 Hour – 1 Hour

Supplies: Red and green laser source, tape, meter stick, blank wall, hair

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Laser Blox

Laser Blox

Step 1

Discussion and Background

When a wave encounters an obstacle, some of the wave bends or diffracts, around the obstacleDiffraction is a phenomenon that describes how light bends as it passes through very narrow slits or around a very small barrier (like a hair). See image to the right showing diffraction (bending) of waves around a “corner”. Thinking of light as a wave, consider that as light passes a very small barrier (like a hair), two distinct wave patterns are formed. Those waves interfere with the each other to either amplify the wave pattern (constructive interference) or dampen the wave pattern (destructive interference).

Diffraction depends upon the Size of obstacle (d) and Size of wave or Wavelength ( λ )

Step 2

Set up

  1. Divide class into two group
  2. Give each group a Laser Blox, a ruler or meter stick, a white sheet of paper and some tape
  3. Have each group choose someone to donate a strand of hair to measure. The hair should be at least 25cm long.
Step 3

Generate and observe a diffraction pattern

Tape the hair to the LASER Blox so that the hair crosses the beam aperture

Set the Laser Blox on a table or other surface approximately 1m from a blank wall or screen

Turn on the laser and observe the diffraction pattern it produces as the laser beam passes the hair.

Light is a wave so it diffracts. In the figure for this step, a beam of light from the left diffracts off a hair travels a distance to the screen where it forms a pattern of light and dark “spots” called a diffraction pattern. The diffraction pattern is a pattern of constructive and destructive interference of the light wave as it passes the obstacle – in this case, a human hair.

Step 4

Introduce the math

Remember, the diffraction pattern depends upon the • d – Size of obstacle • λ – Size of wave

To calculate the width of the hair you will use this formula d = (λ) (L) / W

d = Hair Width or Obstacle Size

λ = Wavelength of light

L = Distance to Screen

W = The distance from the center of one bright spot to the center of the one next to it

Step 5

Collect your data

Take measurements and fill in your data sheet (see .pdf in step 1) for at least 5 pieces of hair

Step 6

Calculate the average width of human hair

Using the formula d = (λ) (L) / W , calculate the width of at least 5 pieces of hair for which you have collected data.

d = Hair Width or Obstacle Size

λ = Wavelength of light

L = Distance to Wall or Screen

W = The distance from the center of one bright spot to the center of the one next to it

Download the FREE Lesson – Measuring Wavelengths V2

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