A perfectly reflecting mirror has an area of $1{\mathrm{cm}}^2$. Light energy is allowed to fall on it for one hour at the rate of $10\mathrm{W} {\mathrm{cm}}^{-2}$. The force that acts on the mirror is

The tendency of light to travel in a straight line is called _____ of light.

(Choose from the following: rectilinear propagation/curvilinear propagation)

Fill in the following blanks with suitable words:

 The image which cannot be projected onto a screen is called_____image.