The electromagnetic spectrum and its uses

Answer Key - Grade 11 Science Worksheet - Challenge Me

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

1. 1.

   A radar pulse goes from Earth to the Moon, 384400 km away, and back. How long does the trip take, Ari?

   2.56 s
2. 2.

   A probe at the Sun–Earth L1 point is 1500000 km away. Bo sends a command and gets the reply. How long is the round trip?

   10.01 s
3. 3.

   A satellite hovers 35786 km up. Esme sends a question up and down to a friend, and the reply goes up and down. How long is the delay?

   0.48 s

4. Read this first

   Five bands (example data)

   band	frequency
   Radio	100 MHz
   microwave	10 GHz
   infrared	30 THz
   visible	500 THz
   ultraviolet	1000 THz

5. 4.

   Using the band table, how many times more energy does a visible photon carry than a microwave photon, Jun?

   • About 50,000 times less, since visible has the shorter wavelength
   • About 50,000 times, since E = hf
   • About 1 ÷ 50,000, since microwaves carry more
   • About 50 times, treating THz and GHz alike
6. 5.

   A 5G phone gets strong 28 GHz signals outdoors but weak ones indoors; lower-frequency signals reach indoors better. Which explains this, Kira?

   • Higher-frequency waves travel slower, so they arrive late
   • Shorter 28 GHz waves are blocked more by walls
   • Walls absorb low frequencies more than high ones
   • Higher-frequency photons carry less energy, so they stop
7. 6.

   Luz builds a half-wave antenna for a 98.1 MHz FM station. About how long should it be?

   • About 1.5 m
   • About 3.1 m, one whole wavelength
   • About 0.76 m, a quarter wavelength
   • About 15 cm, a tenth of a wavelength
8. 7.

   Milo says microwaves cook food from the inside out. Water absorbs 2.45 GHz waves within a centimeter or two. Judge the claim.

   • Supported: microwaves pass through the surface and heat the middle
   • Not supported: the surface absorbs first; heat then conducts inward
   • Supported: the middle absorbs more because it is deeper
   • Not supported: microwaves heat the surface of the food
9. 8.

   Noah says the sky is blue because the air absorbs blue light. Air scatters light roughly as 1/λ⁴. Judge the claim.

   • Not supported: air scatters red light more than it scatters blue
   • Supported: scattering and absorbing are one and the same process
   • Not supported: air scatters blue about 4 times more than red
   • Supported: the blue light we see is what the air lets through
10. 9.

    A thermal camera shows a warm mug in bright yellow and a cold table in blue. What do the colors tell Tala?

    • The colors show how fast the objects are moving
    • The mug gives off yellow light and the table gives off blue light
    • The camera sees the visible colors of each object
    • The software assigns colors to the infrared intensity
11. 10.

    Zee tunes a radio telescope to the 1,420 MHz hydrogen line. What wavelength is that, and why can radio cross dust that blocks light?

    • About 2.1 cm; dust grains are larger than the wavelength
    • About 21 cm; radio waves carry more energy, so they push through
    • About 21 cm; dust grains are far smaller than that wavelength
    • About 21 m; dust grains are far smaller than that wavelength