Define the principal focus of a concave mirror.

What is meant by the radius of curvature of a spherical mirror? How is it related to the focal length of the mirror?

Define the following terms:
$(i)$ Angle of incidence
$(ii)$ Angle of reflection
$(iii)$ Plane of incidence

$(i)$ 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.

Which type of image cannot be obtained by a concave mirror?

Under what condition in an arrangement of two plane mirrors,will the incident ray and the final reflected ray always be parallel to each other,regardless of the angle of incidence? Show the same with the help of a diagram.