What makes things visible to us? Why cannot we see a book which is placed (a) behind a wooden screen, and (b) in a dark room?
Light makes things visible to us. We see an object when light passing through it is reflected.
We cannot see a book which is placed
a- Behind a wooden screen because the wooden screen is opaque so it does not allow light to pass through it.
b- In a dark room because there is no light to be reflected by the book. Thus, due to no reflection, the book is not visible.