Question

1a. Changes in which of the following would affect the focal length of a thin glass lens? You must choose all correct answers.

a. wavelength of light that it is focusing

b. the medium in which the lens is immersed (e.g. air, water)

c. index of refraction of the glass

d. curvature of its 2 refracting surfaces

1b. Changes in which of the following would affect the focal length of a glass mirror with a reflective silver coating on its curved surface? You must choose all correct answers.

a. the medium in which the mirror is immersed (e.g. air, water)

b. index of refraction of the glass

c. curvature of its reflecting surface

d. wavelength of light that it is focusing

Answer 1

1a.

The focal length of a thin lens can be found using the lens makers formula,

           

            1/f = (nl/nm - 1) (1/R1 – 1/R2 )

            Where,

            nl- refractive index of the material of the lens

            nm - refractive index of the material of the surrounding medium

            R1 and R2- radii of curvature of the two refracting surfaces

                Also, the refractive index depends on the wavelength of light used

Hence, following are the factors which affect the focal length of a thin lens.

a. wavelength of light that it is focusing

b. the medium in which the lens is immersed (e.g. air, water)

c. index of refraction of the glass

d. curvature of its 2 refracting surfaces

1b.

The focal length of a spherical mirror is given by the relation,

                Focal length, f = R/2 where R is radius of curvature of the reflecting surface of the mirror.

Hence, the focal length of a glass mirror with a reflective silver coating on its curved surface depends on,

c. curvature of its reflecting surface