### Theory:

Let us discuss the properties of light, such as
• Rectilinear propagation of light
• Reflection
• Speed of light
• Interaction of light with matter
• Spectrum
Rectilinear propagation of light:

What is rectilinear motion?

Rectilinear motion is motion along a straight line.
Light travels in a straight line; it cannot bend the path itself. This is called as the rectilinear propagation of light. Rectilinear propagation is one of the most important properties of light.
The below pictures show the rectilinear propagation of light.

 Light penetration through caves Light penetration through trees Light penetration through a window
The device which helps us to understand the rectilinear propagation of light is a pinhole camera.

Pinhole camera:
A pinhole camera consists of a light-tight box with a pinhole in one end and a piece of film or a screen at the other end.

Pin hole camera - Model
• In the above image, the tree is considered as an object; let us name it as $$XY$$ and $$O$$ will be the hole in the pinhole box.
• When the light rays from the object $$XY$$ fall on the pinhole, it travels in a straight line and reaches the other end of the box which has screen or film.
• When the light rays from the object $$XY$$ fall on the screen, it forms the image $$Y'X'$$.
• The light ray from $$X$$ travels through the hole and reaches the screen. Thus, it forms the image $$X'$$. Likewise, a light ray from $$Y$$ travels through the hole and reaches the screen forming the image $$Y'$$.
• The image produced on the screen is temporary if simple paper is used. The image can be made permanent if the paper is replaced by a photographic plate.
Vintage pinhole camera
Reference:
https://pixabay.com/photos/cave-light-nature-rock-landscape-5229670/
https://pixabay.com/photos/window-views-mountain-summer-1792309/
https://pixabay.com/photos/leaves-sun-sunny-light-penetrates-5936582/