放大鏡why會將東西放大是用what原理

It is because of the refraction of light.

Light from an object is being refracted by a convex lens before entering into the eye. Because of such refraction, the refracted light looks as if it comes from a different position that makes the object appears larger.

放大鏡其實是一塊特透鏡,但光線穿過時,由於特透鏡表面不是平滑的,因此令每個位置折射的角度也不同,最終聚焦後,影像變會變大.

Actually, this is due to refraction of light.
There is a thing called the visual angle. The visual angle is the angle of
elevation or depression from the eye to the object. The greater the visual
angle, the larger the objects appears to be. With a magnifying glass (which
is made of convex lens), light is converged and then passed into our eye. As
the image formed is erect, virtual and magnified, the visual angle is larger.
And this makes the object appears to be larger. (This is known as visual
enlargement).