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9th grade · Science · Unit 25 of 28

Waves & Electromagnetic Radiation

Wave math, light as wave and particle, and how we use waves.

What your child practices

Practices the wave equation (speed = frequency × wavelength), the electromagnetic spectrum and why higher-frequency radiation such as ultraviolet and X-rays can harm living tissue, evidence that light acts as both a wave and a particle, why digital transmission is reliable, and devices that use waves, from solar panels to fiber optics.

New York State Learning Standards learning standard: HS-PS4-1; HS-PS4-2; HS-PS4-3; HS-PS4-4; HS-PS4-5 · the wave equation, digital transmission, the wave and particle models of light, effects of electromagnetic radiation on matter, and devices that use waves

How we explain it

Children can open this short lesson before they practice.

  1. Wave speed = frequency × wavelength. Frequency is measured in hertz (Hz).
  2. Higher-frequency radiation, such as UV and X-rays, carries enough energy to damage cells.
  3. Light acts as a wave and also as particles.

Example: A wave has a frequency of 5 Hz and a wavelength of 2 m. What is its speed? Speed = frequency × wavelength. 5 × 2 = 10. Answer: 10 m/s

Waves & Electromagnetic Radiation in New York

In the New York State Learning Standards, this is unit 25 of 28 in 9th grade Science, after Water, Ice & Landscapes and before Gases, Solutions, Acids & Bases.

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: New York State Education Department (NYSED)

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

    Scientists describe light as…

    • only a wave
    • both a wave and a particle, depending on the experiment
    • only a particle
    • neither a wave nor a particle

  2. Question 2

    A wave has a frequency of 5 Hz and a wavelength of 2 m. What is its speed?

    • 10 m/s
    • 0.4 m/s
    • 7 m/s
    • 2.5 m/s

  3. Question 3

    Fiber-optic cables carry information as…

    • radioactive decay
    • sound inside copper
    • light reflecting along inside glass
    • water pressure

  4. Question 4

    In empty space, all electromagnetic waves travel at…

    • the speed of sound
    • different speeds for each color
    • zero speed
    • the speed of light

  5. Question 5

    Higher-frequency electromagnetic radiation carries…

    • no energy
    • less energy per photon
    • more energy per photon
    • the same energy at every frequency

  6. Question 6

    Wave crests on a lake are 4 m apart, and 2 crests pass a dock each second. What is the wave speed?

    • 2 m/s
    • 8 m/s
    • 6 m/s
    • 0.5 m/s

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