Physical question: Why is the camera exposed?

The camera exposes the film. The film contains some silver salts (such as silver nitrate), which are easily decomposed when exposed to light. The uncombined silver salt is generally colorless, but the silver salt decomposes under illumination to generate silver (the silver thus generated is very fine particles, and the color will not be silvery white, just like iron powder is black, and the color of reflected light will be different due to different particle sizes and refraction). According to the frequency and intensity of exposure on the film, the generated silver particles will have different sizes and colors, and the pictures taken during exposure will appear on the film.

Now to sum up, the question of lz is why it is exposed. Generally speaking, it is because the film contains silver salt, which is easy to decompose when exposed to light.