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 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

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 1 ÷ 50,000, since microwaves carry more
   • 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
5. 4.

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

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

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

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

   • Measure at the same distance with and without the wall, several times each
   • 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 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 carry more energy, so they pass through air
   • X-rays are too bright to be measured from the ground
   • Radio waves travel faster, so they reach the ground
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 software assigns colors to the infrared intensity
    • The mug gives off yellow light and the table gives off blue light
    • The colors show how fast the objects are moving
    • The camera sees the visible colors of each object
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 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