Mirror: a Mirror Is an Object That Reflects Light

Physics Project

HISTORY OF SPHERICAL MIRRORS IN HUMAN CIVILIZATION

Mirror: A mirror is an object that reflects light.

The most familiar type of mirror is the plane mirror, which has a flat screen surface. Curved mirrors are used, to produce magnified or diminished images or focus light or simply distort the reflected image.

Mirrors are commonly used for personal grooming or admiring oneself (where they are also called looking-glasses), decoration, and architecture. Mirrors are also used in scientific apparatus such as telescopes and lasers, cameras, and industrial machinery. Most mirrors are designed for visible light; however, mirrors designed for other wavelengths of electromagnetic radiation are also used.

History[edit]

Seated woman holding a mirror. Ancient Greek Attic red-figure, c. 470–460 BC, National Archaeological Museum, Athens

The first mirrors used by people were most likely pools of dark, still water, or water collected in a primitive vessel of some sort. The earliest manufactured mirrors were pieces of polished stone such as, a naturally occurring volcanic glass. Examples of obsidian mirrors found in Anatolia (modern-day Turkey) have been dated to around 6000 BC. Mirrors of polished copper were crafted in Mesopotamiafrom 4000 BC, and in ancient Egypt from around 3000 BC.[2]

obsidian mirrors

Polished stone mirrors from Central and South America date from around 2000 BC onwards Mirrors made of other metal mixtures (alloys) such as copper and tin speculum metal may have also been produced in China and India.

Metal-coated glass mirrors are said to have been invented in Sidon (modern-day Lebanon) in the first century AD, and glass mirrors backed with gold leaf are mentioned by the Roman author Pliny in his Natural History, written in about 77 AD. The Romans also developed a technique for creating crude mirrors by coating blown glass with molten lead.

Ptolemy conducted a number of experiments with curved polished iron mirrors, and discussed plane, convex spherical, and concave spherical mirrors in his Optics.

Parabolic mirrors were also described by the physicist Ibn Sahl in the 10th century, and Ibn al-Haytham discussed concave and convex mirrors in both cylindrical and spherical geometries, carried out a number of experiments with mirrors,

parabolic mirror

In the 16th century, Venice, a city famed for its glass-making expertise, became a centre of mirror production. Glass mirrors from this period were extremely expensive luxuries.

The invention of the silvered-glass mirror is credited to German chemist justus von liebig in 1835. His process involved the deposition of a thin layer of metallic silver onto glass through the chemical reduction of silver nitrate.

justus von liebig

Manufacturing

of 6 Mirrors are manufactured by applying a reflective coating to a suitable substrate. The most common substrate is glass, due to its transparency, ease of fabrication, rigidity, hardness, and ability to take a smooth finish. The reflective coating is typically applied to the back surface of the glass, so that the reflecting side of the coating is protected from corrosion

In classical antiquity, mirrors were made of solid metal (bronze, later silver) and were too expensive for widespread use by common people; they were also prone to corrosion. Due to the low reflectivity of polished metal, these mirrors also gave a darker image than modern ones, making them unsuitable for indoor use with the artificial lighting of the time (candles or lanterns).

The method of making mirrors out of plate glass was invented by 16th-century on the island of Murano, who covered the back of the glass with mercury, obtaining near-perfect and undistorted reflection.

island of Murano making mirrors

In modern times, the mirror substrate is shaped, polished and cleaned, and is then coated. Glass mirrors are most often coated with silver or aluminium, implemented by a series of coatings

1. Tin(II) chloride 2. Silver 3. Chemical activator 4. Copper

5. Paint

Effects

• In a plane mirror, a parallel beam of light changes its direction as a whole, while still remaining parallel; the images formed by a plane mirror are virtual images, of the same size as the original object.

• In a concave mirror, parallel beams of light become a convergent beam, whose rays intersect in the focus of the mirror. Also known as converging mirror

• In a convex mirror, parallel beams become divergent, with the rays appearing to diverge from a common point of intersection "behind" the mirror.

• Spherical concave and convex mirrors do not focus parallel rays to a single point due to spherical aberration. However, the ideal of focusing to a point is a commonly used approximation. Parabolic reflectors resolve this, allowing incoming parallel rays (for example, light from a distant star) to be focused to a small spot; almost an ideal point. Parabolic reflectors are not suitable for imaging nearby objects because the light rays are not parallel.

Applications

A cheval glass

Reflections in a spherical convex mirror. A mirror on a racing car.

Personal grooming

Mirrors are commonly used as aids to personal grooming. They may range from small sizes, good to carry with oneself, to full body sized; they my be handheld, mobile, fixed or adjustable.

Safety and easier viewing

Convex mirrors

Convex mirrors provide a wider field of view than flat mirrors, and are often used on vehicles, especially large trucks, to minimize blind spots. They are sometimes placed at road junctions, and corners of sites such as parking lots to allow people to see around corners to avoid crashing

Mouth mirrors or "dental mirrors"

Mouth mirrors or "dental mirrors" are used by dentists to allow indirect vision and lighting within the mouth. Their reflective surfaces may be either flat or curved. Mouth mirrors are

of 6 also commonly used by mechanics to allow vision in tight spaces and around corners in equipment.

Decoration

Mirrors are frequently used in interior decoration and as ornaments:

 Mirrors, typically large and unframed, are frequently used in interior decoration to create an illusion of space and amplify the apparent size of a room They come also framed in a variety of forms, such as the pier glass and the over mantel mirror.

 A decorative reflecting sphere of thin metal-coated glass, working as a reducing wide-angle mirror, is sold as a Christmas ornament called a bauble.