Optics and Lenses

A convex lens of focal length 5 cm is preferred to read small letters of dictionary. To view the small letters in a dictionary, a convex lens of small focal length is suitable. This is because for working as a simple microscope, convex lens of small focal length is needed. The image is formed at the near point (D = 25 cm) for easy viewing.

A magnifying glass (convex lens) needs a short focal length to produce strong magnification - shorter focal length = higher magnification power.

A concave lens is thinner at the center than at the edges and causes parallel light rays to diverge (spread out) after passing through it. This diverging property is why concave lenses are used to correct myopia. Convex and planoconvex lenses are converging lenses, while cylindrical lenses correct astigmatism.

convex lens is used for correcting the defect of long sight

Yes, it is made up of two imaginary spheres. One curved surface extends towards left and forms a sphere and the other towards right. Hence, has two centre of curvatures.

Yes, biconcave lens has two concave lenses joint together, thick at edges and thin in the middle.

Yes, point at which parallel rays of light converge in a concave lens and parallel rays of light diverge from the point is called focus or principal focus of the lens.

Yes, every part of a lens forms a complete image. So, complete image will be formed, but its intensity will be less.

Yes, it is the correct answer. Both b and d are false. In convex lens, edges are thin and  the lens is thick in middle. Distance between the focus and optical center is the focal length.

Yes, in this case the ray diagram in both the lenses is same.

Yes, when lens is immersed in a liquid whose refractive index is greater than refractive index of material of lens then it will change its nature and become concave lens and thus it will start diverging the rays rather than focusing them on a single point.

Convex lenses are converging lenses that bring light rays to a focus. Long sightedness (hypermetropia) occurs when the eyeball is too short or the lens too weak, causing images to focus behind the retina. A convex lens adds focusing power to bring images forward onto the retina. Short sightedness requires concave (diverging) lenses instead.

Long sight (hyperopia) occurs when the eyeball is too short or the cornea has too little curvature, causing light to focus behind the retina. A convex lens converges light rays before they enter the eye, moving the focal point forward onto the retina. Concave lenses are used for myopia (short sight), while plane lenses have no optical power.

A simple microscope consists of a short focus convex lens because shorter focal length provides higher magnification. The convex lens converges light rays from the object, creating a magnified virtual image when the object is placed within the focal length. A concave lens always produces diminished images, and long focal length would give lower magnification.

Astigmatism occurs when the cornea or lens has different curvature in different directions, causing blurred vision. Cylindrical lenses have different focal powers in different meridians, which compensates for this irregular curvature and restores clear vision.