Light and sound crossword puzzle

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Across
  1. 3. Sound does not travel through it
  2. 4. A sound wave is made up of this and rarefactions
  3. 7. A sound wave is not transverse but
  4. 10. Sound travels fastest inside this
  5. 12. All of the light passes through these objects
  6. 13. Acts like a screen in the eye, made up of photosensory cells
  7. 14. Are created when an object blocks a path of light
  8. 16. In a mirror the angle of incidence is equal to this
  9. 17. Light does not pass all of it from these objects
  10. 20. On a dark day light rays are __________ by clouds
Down
  1. 1. No light passes from these objects
  2. 2. At a certain distance, it produces an image that is diminished and inverted
  3. 5. Sound is produced by this
  4. 6. This works similarly to an eye
  5. 8. These produce musical sounds
  6. 9. A sound can have a high one or a low one
  7. 11. The coloured part of the eye that is made of muscle tissue
  8. 15. The units of Sound
  9. 18. Objects that give out light, like the sun
  10. 19. The organ that helps us to hear a sound
  11. 20. Smooth shiny surfaces have very few of these
  12. 21. The organ that helps us to see an image