The electromagnetic spectrum and its uses

Answer Key - Grade 11 Science Worksheet

Circle the best answer, or write your answer on the line.

1. 1.

   A germicidal lamp gives off 254 nm photons. With hc = 1,240 eV·nm, what is each photon's energy in eV, Ari?

   4.88 eV
2. 2.

   A red LED gives off 620 nm photons. With hc = 1,240 eV·nm, what is each photon's energy in eV, Bo?

   2 eV
3. 3.

   A lab X-ray source gives off 0.124 nm photons. With hc = 1,240 eV·nm, what is each photon's energy in eV, Esme?

   10,000 eV
5. 4.

   Using the device table, which wave has the longest wavelength, and about how long is it, Jun?

   • FM radio, about 3.1 m
   • Microwave oven, about 12 cm, since GHz is the biggest unit
   • FM radio, about 3.1 km
   • FM radio, about 0.33 m
6. 5.

   A building is 20 m wide. Using the device table, which wave bends (diffracts) most around it, Luz?

   Use the picture in question 4.

   • Wi-Fi, since it passes through walls instead of bending
   • The germicidal lamp, since higher-energy waves bend more
   • FM radio: its 3 m wavelength is closest to the building's size
   • The TV remote, since infrared goes around corners
7. 6.

   A microwave oven runs at 2.45 GHz. What are its wavelength and the spacing of hot spots (half a wavelength), Milo?

   • Wavelength 12.2 cm; hot spots 12.2 cm apart, one wavelength
   • Wavelength 6.1 cm; hot spots 3.1 cm apart
   • Wavelength 12.2 m; hot spots about 6.1 m apart
   • Wavelength 12.2 cm; hot spots about 6.1 cm apart
8. 7.

   A microwave door has a mesh with 2.0 mm holes. Microwaves are 12.2 cm; light is about 500 nm. Why can Noah see in but microwaves stay in?

   • Holes are far smaller than the microwaves but far larger than light waves
   • The mesh absorbs microwaves, because they carry more energy than light
   • Light is brighter than microwaves, so it overpowers the metal mesh
   • Microwaves travel slower than light, so the small holes stop them
9. 8.

   Ren compares two 1.0 m telescopes: one sees 500 nm light, one sees 21 cm radio waves. Which resolves finer detail, and by what factor?

   • The optical one, about 42 times finer
   • The radio one, since longer waves reach farther
   • The optical one, about 420,000 times finer
   • Neither: both have a 1.0 m diameter
10. 9.

    Wien's law: λ max = 2.898 × 10⁻³ m·K ÷ T. Skin is 310 K and the Sun 5,772 K. Which waves suit Tala's night camera for people?

    • Radio: skin peaks near 9.3 mm
    • Infrared: skin peaks near 9.3 µm
    • Ultraviolet: warm bodies give off UV
    • Visible: skin peaks near 0.50 µm
11. 10.

    The James Webb telescope observes infrared. Why does that help it see the most distant galaxies, Zee?

    • Infrared is the one kind of light that crosses space
    • Infrared photons carry more energy, so they travel farther
    • Cosmic expansion stretches their light into the infrared
    • Distant galaxies give off infrared light and nothing else