In other words, an x-ray is a light that we cannot see or feel. Even though we cannot see x-rays with our eyes, they can still effect the cells in our bodies. X-rays penetrate objects. Bones, on the other hand, are made of dense material and make it harder for x-rays to pass through. This is why bones appear white on the doctors exposed x-ray film.
Lets now take a look at how film works.
Film is a thin layer of photo-sensitive chemicals that are sometimes coated in plastic to protect from outside elements. When various wavelengths of light penetrate the film, they initiate chemical changes. This is then printed onto paper through a photo development process. Now that that's behind us, let's see how x-rays effect film. For example, when film comes in contact with x-rays, it effects it in the same way that a very bright light source would.