If your stomach does not contain a light source how does the doctor see inside your stomach using an endoscope?
your stomach isn't what produces the light source.Light is
actually directed into the body through the endoscope and the image
is transmitted back to the operator. this uses totla internal
reflection,(when waves move from one medium to another with
different refractive indices). if you need detailed answers then u
should probably research the coherent and non-coherent bundles in
an endescope. this also relates to total internal reflection as
they are optical fibres.
i
cheers
total