Question

A concave lens is used in:
A. simple camera
B. spectacles for the correction of short sightedness
C. magnifying glass
D. Vehicles to see objects on rear side

Answer 1

Hint: Think what a concave lens is and describe the structure. It is diverging in nature, and can create magnified images. Apply this to each option and check whether they fit into each.

Complete step by step answer

A concave lens is fabricated using two concave mirrors. The centre portion of the mirror is inwardly curved. So the middle part is thinner compared to the edges of the lens. It is an optical device which transmits light to pass through it.

When the light rays fall on it, they will undergo refraction. Due to this refraction of light, the emitted light rays appear to have diverged. Hence, the name- diverging lens. Its main property is magnification.

There are so many applications of a concave lens.

a. It is used in cameras: Both the concave lens and the convex lens is used in a camera. The combination of both will help the functioning of the camera. The images captured by the convex lens are distorted. To eliminate this effect, a concave lens is used.

b. It is used in spectacles for the correction of short sightedness (myopia): Short sightedness or myopia is a condition in which the person can see the objects within a short-range. But objects which are at a long distance appear to be blurry. Since the eyeball is too long, the light won’t fall at the focus of an object coming from a long distance. Then a concave lens is used, which will help to fall the light on the retina.

c. A concave lens is used as a magnifier: Since it diverges the light rays, the image formed by the concave lens is always enlarged and upright. So it is easy to use a concave lens as a magnifier. It is used in telescopes to view the magnified image of celestial objects.

d. Rear side mirror in the vehicle: Here, a convex mirror is used. The image created by a convex mirror is erect, enlarged and diminished; it is useful to make a side rear view mirror.

So options A, B and C are correct.

Note: Please remember that light rays emitted from a concave appear to be diverging from the focus. The focal length of a concave lens is always taken as negative whereas positive in the case of a convex lens. Other than the above mentioned they are used in flashlights, peepholes, binoculars etc.