Spherical Mirrors, Lenses, Human Eye, and Light: Key Concepts

Sign Convention for Reflection by Spherical Mirrors

1. The object is always placed on the left of the mirror.
2. All distances parallel to the principal axis are measured from the pole of the mirror.
3. Distances measured perpendicular to and above the principal axis are taken as positive.
4. Distances measured perpendicular to and below the principal axis are taken as negative.
5. The focal length of a concave mirror is negative.

Image Formation by a Concave Lens

1. If the object is at infinity, the image is formed at the focus of the lens on the same side of the lens as the object. It is virtual, erect, and highly diminished.
2. If the object is at any finite distance from the lens, the image is formed on the same side of the lens as the object and between the focus and the optical center of the lens. It is virtual, erect, and diminished. The image distance is less than the object distance.

The Human Eye and its Similarities to a Camera

• The retina in the human eye is similar to the photographic film in a camera.
• The pupil in the human eye is similar to the aperture in a camera.
• The ciliary muscles adjust the size and curvature of the eye lens.
• The refraction of light is responsible for the working of the eye.

Myopia (Nearsightedness)

Myopia, or nearsightedness, is a vision defect in which a person can see nearby objects distinctly but is unable to see distant objects clearly. In this case, the image of a distant object is formed in front of the retina instead of on the retina.

Hypermetropia (Farsightedness)

Hypermetropia, or farsightedness, is a vision defect in which a person can see distant objects clearly but is unable to see nearby objects clearly. In this case, the image of a nearby object would fall behind the retina instead of on the retina.

Simple Microscopes in Watch Repair

Watch repairers use simple microscopes because when an object is placed within the focal length of a magnifying glass (a convex lens), a magnified and erect image is obtained on the same side of the lens as the object. By adjusting the distance between the object and the lens, the image can be obtained at the distance of distinct vision. Thus, a watch repairer can see the minute parts of a watch more clearly with the aid of a magnifying glass than with the naked eye, without any strain on the eye.

Dispersion of Light

The phenomenon of splitting light into its component colors is called dispersion. The band of colored components of a light beam is called a spectrum. The different colors of light in the spectrum of white light are violet, indigo, blue, green, yellow, orange, and red.

Adverse Effects of Ozone Depletion

1. When the ozone layer is depleted, the ultraviolet (UV) radiation from the sun can reach the Earth's surface in greater proportion.
2. This results in damage to animal and plant life on Earth.
3. Ultraviolet rays cause skin cancer and cataracts in human beings.
4. The ozone hole is observed in the stratosphere above Antarctica.