octagon

(a)  

decagon

(a)  

diagonal

(a)  

interior angel

(a)  

exterior angel

(a)  

deposition

(a)  

ultrasound

(a)  

infrasound

(a)  

decibel

(a)  

transparent

(a)  

pinhole imagining

(a)  

normal

(a)  

reflected ray

(a)  

incident ray

(a)  

angle of reflection

(a)  

diffuse reflection

(a)  

virtual image

(a)  

convex mirror

(a)  

concave mirror

(a)  

angle of refraction

(a)  

refractive index

(a)  

Snell's law

(a)  

triangular prism（mirror）

(a)  

total internal reflection

(a)  

dispersion of light

(a)  

infrared ray

(a)  

ultraviolet

(a)  

concave lens

(a)  

convex lens

(a)  

focal length

(a)  

focal point

(a)  

magnifying glass（lens）

(a)  

projector

(a)  

microscope

(a)  

eyepiece（eye lens）

(a)  

objective

(a)