Magnification is the ratio of which of the following?

What will be the angle of refraction for a light ray incident normally at the surface (in $^{\circ}$)?

What is the power of a convex lens with a focal length of $20 \text{ cm}$?

$(i)$ Under what condition does a concave mirror produce a virtual and magnified image? Draw a labelled ray diagram to show the formation of the image in the above case. Also,state the position of the object to produce a magnified and real image.
$(ii)$ $A$ ray of light moving along the principal axis is falling on a concave mirror. Draw the path of the reflected ray. Also,state the values of the angle of incidence and reflection in this case.

At what position should an object be placed in front of a concave mirror to obtain a magnification of $(- 2)$?

$A$ virtual image cannot be focused on a screen. Yet when we see a virtual image,we obviously bring it to the screen that is the retina of our eyes. Is this a contradiction?