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. Read this first

   Five bands (example data)

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

4. 3.

   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 times, treating THz and GHz alike
   • About 50,000 times, since E = hf
   • About 1 ÷ 50,000, since microwaves carry more
5. 4.

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

   • Shorter 28 GHz waves are blocked more by walls
   • Higher-frequency waves travel slower, so they arrive late
   • Higher-frequency photons carry less energy, so they stop
   • Walls absorb low frequencies more than high ones
6. 5.

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

   • Not supported: the surface absorbs first; heat then conducts inward
   • Supported: the middle absorbs more because it is deeper
   • Supported: microwaves pass through the surface and heat the middle
   • Not supported: microwaves heat the surface of the food
7. 6.

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

   • Supported: the blue light we see is what the air lets through
   • Not supported: air scatters blue about 4 times more than red
   • Not supported: air scatters red light more than it scatters blue
   • Supported: scattering and absorbing are one and the same process
8. 7.

   Pia wants to test whether a wall weakens a Wi-Fi signal. Which design is best?

   • Measure the router's label power and compare it with the wall's thickness
   • Measure once in each room, wherever the signal is easiest to reach
   • Measure at the same distance with and without the wall, several times each
   • Measure with the wall in place, then again much farther from the router
9. 8.

   Why do X-ray telescopes orbit above the atmosphere, while many radio telescopes work on the ground, Ren?

   • Air absorbs X-rays but passes many radio waves
   • Radio waves travel faster, so they reach the ground
   • X-rays are too bright to be measured from the ground
   • Radio waves carry more energy, so they pass through air
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 camera sees the visible colors of each object
    • The software assigns colors to the infrared intensity
    • The mug gives off yellow light and the table gives off blue light
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 21 m; dust grains are far smaller than that 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 2.1 cm; dust grains are larger than the wavelength