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8th grade · Science · Unit 4 of 13

Light & Radiation

Waves, the spectrum and how light behaves

What your child practices

Wavelength and frequency, the electromagnetic spectrum from radio waves to gamma rays and what each is used for, reflection, refraction and color, and staying safe from UV radiation.

Texas Essential Knowledge and Skills (TEKS) teks student expectation: 8.8(A); 8.8(B) · the electromagnetic spectrum, wavelength and frequency, and uses of electromagnetic waves

How we explain it

Children can open this short lesson before they practice.

  1. The electromagnetic spectrum, from longest to shortest wavelength: radio, microwave, infrared, visible light, ultraviolet, X-ray, gamma.
  2. Shorter wavelength means higher frequency and more energy.
  3. Light reflects off mirrors and bends (refracts) when it passes into a new material. Block UV with sunscreen and shade.

Example: Which has a longer wavelength: radio waves or X-rays? Radio waves are at the long end of the spectrum. X-rays are near the short end. Answer: radio waves

Light & Radiation in Texas

In the Texas Essential Knowledge and Skills (TEKS), this is unit 4 of 13 in 8th grade Science, after Forces, Motion & Momentum and before Cycles & Succession.

Gradelings describes a child's practice on this unit as Beginning, Approaching, Meeting or Exceeding (Four practice steps). That reflects practice, not a report-card mark: the teacher decides the mark.

Source: Texas Education Agency (TEA)

Sample questions

A taste of this unit. In the app, questions change every time and get easier or harder to match your child.

  1. Question 1

    When light bends as it passes from air into water, this is called…

    • refraction
    • reflection
    • radiation
    • absorption

  2. Question 2

    As the frequency of a wave increases, its wavelength…

    • increases
    • disappears
    • stays the same
    • decreases

  3. Question 3

    Longer or shorter wavelength than visible light? Sort each radiation.

    Sort into: 〰️ Longer than visible light · ⚡ Shorter than visible light

    • 🌡️infrared
    • ☢️gamma rays
    • ☀️ultraviolet
    • 🍿microwaves
    • 🪫UV from a tanning lamp
    • 📶Wi-Fi signals
    • 🩻X-rays
    • 📻radio waves

  4. Question 4

    Which travels fastest?

    • light
    • a car
    • sound
    • a jet plane

  5. Question 5

    Put these types of electromagnetic radiation in order from the longest wavelength to the shortest.

    • 🌈Visible light
    • 🍿Microwaves
    • ☀️Ultraviolet
    • 📻Radio waves

  6. Question 6

    Which has the shortest wavelength?

    • infrared
    • microwaves
    • visible light
    • gamma rays

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