What is the effect on the wavelength of light when it travels from a rarer to a denser medium?

$(a)$ Write the relation between $u, v, f$ for lenses and for mirrors,where $u, v, f$ are object distance,image distance,and focal length respectively.
$(b)$ The magnification produced by a concave mirror is $m = +4$. Write the information about the image given by this statement.
$(c)$ Draw a ray diagram for the following and show the formation of the images in the case of a concave mirror when the object is placed:
$(i)$ Between the pole and the focus point.
$(ii)$ At the centre of curvature.

From which point of a lens are all the distances measured?

Define the term power of a lens.

Which type of mirror can produce a virtual image?

Which of the following statements is true for light waves?