The Electromagnetic Spectrum · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.
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The Electromagnetic Spectrum

Science · Waves, Light & Sound · ages 12-13
Name ______________________   Date ____________

  1. Which pair gives a use and a possible hazard of radio waves?

    • Disinfecting water; exposure can damage skin and eyes
    • Forming bone images; exposure can ionize atoms and damage cells
    • Carrying broadcasts; very intense exposure can heat tissue
    • Carrying broadcasts; tissue damage comes from directly ionizing atoms

  2. Which region can human eyes detect directly?

    • Infrared radiation
    • Visible radiation
    • Ultraviolet radiation
    • Microwave radiation

  3. Intense visible light, such as a laser beam, can damage eyes.

    Circle one:   True   False

  4. How does an X-ray's speed through empty space compare with a radio wave's speed?

    • The X-ray travels faster through empty space
    • Both have the same speed through empty space
    • The radio wave travels faster through empty space

  5. Which region has a lower frequency and a longer wavelength than visible light in the usual spectrum chart?

    • Ultraviolet
    • Gamma rays
    • X-radiation
    • Infrared

  6. Tissue absorbs energy at a constant rate from an unchanged X-ray beam. Exposure lasts 20 seconds instead of 10 seconds. How does the absorbed energy change?

    • It doubles because exposure time doubles.
    • It halves because the energy is spread over twice the time.
    • It stays unchanged because the beam's frequency stays unchanged.
    • It increases by half because 10 seconds is half of 20 seconds.

  7. Which pair correctly matches a spectrum region with a use?

    • Microwaves - heating food in microwave ovens
    • Infrared - forming images of bones through body tissue
    • Gamma rays - carrying signals between WiFi devices

  8. A UV lamp disinfects water. A learner says its useful job makes it safe to look directly at the lamp. Which response fits?

    • UV can damage microbes, but human eyes are protected because they are much larger than microbes.
    • UV can damage microbes and eyes, so this useful lamp still needs protective measures.
    • UV is invisible, so it cannot transfer enough energy to damage a person's eyes.
    • UV helps skin make vitamin D, so a lamp used for disinfection should also be safe to view.

  9. An EM wave has wavelength 0.18 m in a vacuum. Its frequency triples while its speed stays unchanged. What is the new wavelength in metres?

    Answer: ______________

  10. Leo says an oven heats food quickly, so each microwave photon must have more energy than a UV photon. Which correction fits?

    • Microwave photons have more energy because rapid heating sets the energy of each individual photon.
    • UV photons have more energy because their frequency is higher; heating also depends on absorbed energy each second.
    • Both photons have equal energy because their shared vacuum speed sets the energy of each individual photon.
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Answer key

For grown-ups. Fold this page away before handing over the rest.

The Electromagnetic Spectrum W1-mt_XSp-S0wter-s1

  1. Carrying broadcasts; very intense exposure can heat tissue · Radio waves carry broadcasts. Very intense exposure can heat tissue and cause burns; that condition does not describe every radio exposure.
  2. Visible radiation · Human eyes detect visible light directly. Instruments can detect other regions and turn measurements into visible displays.
  3. True · Visible light helps us see, but an intense beam can injure eyes. A useful region is not harmless at every exposure.
  4. Both have the same speed through empty space · Both are EM waves, so they share the same vacuum speed, approximately 300,000,000 m/s. Their different frequencies do not change that speed.
  5. Infrared · Infrared lies below visible light in frequency. At the shared vacuum speed, its lower frequency corresponds to a longer wavelength.
  6. It doubles because exposure time doubles. · At the same absorption rate, 20 seconds gives twice the absorbed energy of 10 seconds. The beam's frequency does not need to change.
  7. Microwaves - heating food in microwave ovens · Microwave ovens transfer microwave energy to food. Water in the food absorbs some of this energy, and the food warms.
  8. UV can damage microbes and eyes, so this useful lamp still needs protective measures. · UV can damage cells in microbes and in people. Its use for disinfection does not remove the risk of skin or eye damage.
  9. 0.06 · At fixed speed, tripling frequency divides wavelength by three. The new wavelength is 0.18 ÷ 3 = 0.06 m.
  10. UV photons have more energy because their frequency is higher; heating also depends on absorbed energy each second. · UV has a higher frequency, so each UV photon has more energy. Heating rate also depends on how much energy is absorbed each second.
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