| Difficulty | Secondary School | High school/other |
| ★ | Basic | Easy |
| ★★ | Demanding | Basic |
| ★★★ | Demanding | |
| ★★★★ | Difficult | |
| ★★★★★ | Very difficult |
In the video, the light of the laser hits the diffraction grating. How many slits per millimeter can the diffraction grating contain.
Answer: 480 – 520 pieces ($500\pm20$ gap/mm)