Question

A lens is a transparent optical medium bounded by two surfaces; at least one of which should be spherical. Applying the formula of image formation by a single spherical surface successively at the two surfaces of a thin lens, a formula known as lens maker’s formula and hence the basic lens formula can be obtained. The focal length (or power) of a lens depends on the radii of its surfaces and the refractive index of its material with respect to the surrounding medium. The refractive index of a material depends on the wavelength of light used. Combination of lenses helps us to obtain diverging or converging lenses of desired power and magnification.

A beam of light coming parallel to the principal axis of a convex lens L₁ of focal length 16 cm is incident on it. Another convex lens L₂ of focal length 12 cm is placed coaxially at a distance 40 cm from L₁. The nature and distance of the final image from L₂ will be ______.

पर्याय

• real, 24 cm

• virtual, 12 cm

• real, 32 cm

• virtual, 18 cm

Answer 1

A beam of light coming parallel to the principal axis of a convex lens L₁ of focal length 16 cm is incident on it. Another convex lens L₂ of focal length 12 cm is placed coaxially at a distance 40 cm from L₁. The nature and distance of the final image from L₂ will be real, 24 cm.

Explanation:

The image will also be formed at 2F, as the object for L₂ is located at 2F.

The point 'O' at which the image of L₁ is formed is the center of curvature of the lens L₂. Therefore, the final image will be generated at a distance of 24 cm from the lens, and the nature will be authentic.