#29e MC16
#wave
#30e MC18
#statinonary wave
#39e MC19
#echo
#31e MC20
#refraction #refractive index
#32e MC21
#dispersion of light
#37e MC22
#lens formula
#33e MC23
#diffraction grating
#wave
#statinonary wave
#echo
#refraction #refractive index
#dispersion of light
#lens formula
#diffraction grating