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 highest photon energy, and why, Kira?

   • FM radio, since the longest waves carry the most energy
   • The TV remote, since 940 is the biggest number
   • The germicidal lamp: 254 nm is the shortest wavelength
   • The microwave oven, since 2.45 GHz is a big number
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
   • FM radio: its 3 m wavelength is closest to the building's size
   • The germicidal lamp, since higher-energy waves bend more
   • 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 cm; hot spots about 6.1 cm apart
   • Wavelength 12.2 m; hot spots about 6.1 m 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
   • Microwaves travel slower than light, so the small holes stop them
   • Light is brighter than microwaves, so it overpowers the metal mesh
9. 8.

   Water absorbs 4.19 J per gram per °C. An oven puts 700 W into 250 g of water for 60 s. What is the temperature rise, Pia?

   • About 40,000 °C, using 0.25 kg with joules per gram
   • About 0.67 °C, leaving out the time
   • About 40 °C
   • About 80 °C, doubling the power
10. 9.

    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 radio one, since longer waves reach farther
    • The optical one, about 420,000 times finer
    • The optical one, about 42 times finer
    • Neither: both have a 1.0 m diameter
11. 10.

    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
    • Visible: skin peaks near 0.50 µm
    • Infrared: skin peaks near 9.3 µm
    • Ultraviolet: warm bodies give off UV