Light & Mirror

LIGHT

QUALITATIVE CHARACTERISTICS OF IMAGES

• light EM radiation is visible to the human eye and is responsible for the sense of sight
• aspect of radiant energy which an observer is usually aware of
• light is an EM wave and is included in the EM spectrum

PROPERTIES OF LIGHT

Reflection

Irregular/Diffuse Reflection

• allows us to see objects from any angle
• produced by rough surfaces that tend to reflect light in all directions

Regular/Specular Reflection

• light that strikes in smooth and shiny surface, is reflected in one direction
• light reflected from a smooth surface at a definite angle

Refraction

• bending of light as it travels from a transparent medium of a different optical density

REFLECTION OF LIGHT IN MIRRORS

• Law of Reflection states:

– incident ray, reflected ray, and the normal line all lie in the same plane

– angle of incidence is equal to the angle of reflection

• in symbols:

θi = θr

Periscope

• instrument for observation over, around or through an obstacle

  

REFLECTION IN PLANE MIRROR

Characteristics of images formed by a plane mirror:

1. image is virtual
2. same size as the object
3. same orientation as the object
4. same distance from the mirror as the object

Reflection of light

• phenomenon by which a ray of light changes the direction of propagation when it strikes a boundary between different media through which it cannot pass

MIRRORS

• smooth reflecting surfaces usually made up of polished metal or glass that have been coated with some metallic substances and can be flat or curved.

Plane Mirrors

• have flat surfaces

Spherical Mirrors

• most curved mirrors because their shape follows the surface of a sphere
• either concave or convex

TWO KINDS OF SPHERICAL MIRRORS

Concave Mirror

• reflects light inward to one focal point

• used to focus light

• converging mirror – has a reflecting surface that is recessed inward (away from the incident light)

• side of the mirror that bends inward is used as a reflecting surface

  

Convex Mirror

• side of the spherical surface that bends outward is used to reflect light

• diverging mirror – curved mirror in which the reflective surface bulges towards the light source

• reflect light outwards

• are not used to focus light

  

TWO TYPES OF IMAGES FORMED BY REFLECTING SURFACES

Real Image

• formed when light rays actually meet after reflection
• can be formed on a screen
• inverted with respect to the object
• e.g. image of a distant object formed by a concave mirror

Virtual Image

• formed when light rays do not actually intersect after reflection but they appear to diverge from the mirror
• cannot be formed on a screen
• erect with respect to the object
• e.g. image of an object formed by a convex mirror

IMAGE FORMATION BY PLANE MIRROR

• plane mirror makes an image of objects in front of the mirror; image appears to be behind the plane in which the mirror lies

• an image is formed by reflection when two or more reflected rays of a point meet at a single point

• image is formed at the point of intersection of the reflected rays

  

IMAGE FORMED BY CURVED MIRRORS

• Center of Curvature, C

– center of sphere whose surface forms the curved mirror

• Focal Point, F

– where the light rays meet

• Vertex, V

– point where the principal axis meets the mirror

• Principal Axis

– straight line passing through the center of curvature to the mirror

• Focal length, f

– distance from the focal point to the vertex

• Radius of Curvature, R

– distance from the vertex to the center of the curvature

• focal length would be one-half the radius of curvature

IMAGE FORMED IN CONCAVE MIRRORS

IMAGE FORMED IN CONVEX MIRRORS

APPLICATIONS OF CONCAVE AND CONVEX MIRRORS

CONCAVE MIRROR

• also known as a converging mirror, has a reflecting surface which collects light inward and focuses it to one focal point. This type of mirror is what the dentist used in magnifying the area behind your teeth to check on cavities and tooth decay.
• For illuminating purposes, you can see concave mirrors used in headlamps, flashlights and spotlights. In these devices, the light rays that gathered from a small source of the mirror are collected and directed outward in a beam. Small light source bounded by a concave mirror flashes a brighter beam.

CONVEX MIRROR

• also known as diverging mirror, is another type of spherical mirror which has the outer bulging surface that reflects light instead of the inner one. It has a wider view field compared to a concave mirror. This makes bigger objects appear to be smaller than their original form.
• A car’s side mirrors enable the driver and its passenger to see the vehicles behind. Also, while in mall supermarkets and in some convenience stores, you may notice mirrors hanging on corners from which you can see your reflection and those of other people. These are just some of the applications of convex mirrors.

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