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?
The light coming from the source falls on the object and reflects back into our eyes and our eye lens form an image of it which is virtual and inverted.
(a) We cannot see book placed behind wooden screen because wooden screen is opaque and light cannot pass through it to enable us to see.
(b) In a dark room, there is no light, so light cannot pass through the eye to enable us to see.