Reflection of Light overview


Common Misconception

Fact

Light travels along any path.

Light travels in straight line.

We cannot see reflections of objects in water.

The surface of water (when still) can act like a mirror and change path of light like a reflecting surface.

A mirror is transparent.

A mirror is opaque.

A wet surface reflects more light than a dry surface.

A wet surface absorbs more light than a dry surface, hence looks darker.

 

Light can be defined as a form of energy. It helps us to see things. Photosynthesis is one of the process by which plants prepare their own food for their growth in the presence of sunlight. Light energy is an invisible form of energy that causes sensation of vision.



Source of light

An object that emits light is called a source of light. The sun, the stars and the glowworm are some of the natural sources of light, whereas, oil lamps, candles, electric lights are examples of artificial sources of light.

Objects that give off their own light are called luminous objects and the objects that do not give off their own light are called the non-luminous objects. The non-luminous objects can be seen due to the light reflected by luminous objects.

Optical Medium

The term medium is used for any substance through which light might pass.

Example Glass, water, air etc.,

Transparent medium

Substances that allow most of the light to pass through them are called transparent substance. We can see through them clearly. A transparent substance is called an optical medium.

Example

Glass, water, air etc.,

Translucent medium

Substances which allows only a part of the light to pass through it and through which object cannot be distinctly seen.

Example

Butter paper, Paraffin wax, greased paper, ground glass etc.,

Opaque medium

Opaque object is one that does not allow any light to pass through it. They reflect or absorb all the light that falls on them. We cannot see through them.

Example

Wood, stone, rubber, walls, books etc.,

 Homogeneous Medium

An optical medium which has different composition at different points is called heterogeneous medium.

Example

Air, muddy water, fog, mist, smoke of clouds etc., 

Point source of light

If a screen with a pin hole is placed in front of a lighted bulb then a point source of light is obtained. From the point source, light propagates uniformly in all directions.

A ray

Light from a point source spreads out in all directions. The directions of a very narrow path of light are known as a ray of light.

A ray of light is represented by a straight line with an arrow head. The arrow head on it gives the direction of light.

Beam of Light

A collection of rays of light is called a beam of light. A beam of light is classified into three kind’s viz. parallel beam of light, convergent beam of light, divergent beam of light.

Parallel beam of light

These rays of light are parallel to each other such that the distance between the rays remains same. Light from distant objects gives a parallel beam of light.

Convergent beam of light

In a convergent beam of light, the light rays meet at a point.

Divergent beam of light

In a divergent beam of light, the light rays spread out from a point.

Reflection

The phenomenon by virtue of which incident light energy is partly or completely sent back into the same medium from which it is coming after being obstructed by a surface is called reflection.



Some terms related with reflection

Point of incidence

The point at which the incident ray strikes the reflecting surface is called the point of incidence.

Incident ray

A ray of light which falls on the reflecting surface is called incident ray.

Reflected ray

The light ray obtained after reflection from the surface in the same medium in which the incident ray is travelling is called the reflected ray.

Normal

The perpendicular drawn to the surface at the point of incidence is called the normal.

Angle of incidence

The angle which the incident ray makes with the normal at the point of incidence is called angle of reflection. It is denoted by letter i.

Angle of reflection

The angle which the reflected ray makes the normal at the point of incidence called angle of reflection. It is denoted by letter r.

Glancing angle of incidence

The angle between the incident ray and the reflecting surface is called the ‘glancing angle of incidence’. It is denoted by letter gi.

Glancing angle of reflection

The angle between the reflecting surface and the reflected ray is called the ‘glancing angle of reflection’. It is denoted by gr.

Plane of incidence

The plane containing the incident ray and the normal is called plane of incidence.

    Plane of reflection

The plane containing the reflected ray the normal is called plane of reflection.

Laws of Reflection

a)    The angle of incidence ‘I’ is equal to the equal of reflection ‘r'.

b)    The incident ray, the reflected ray and the normal to the surface at the point incidence all lie on the same plane.

Types of Reflection

There are two types of reflection: Regular (or specular) and Diffuse (or irregular) reflections. In regular reflection, the light is reflected in one direction only. This occurs on smooth surfaces such as mirrors. In irregular reflection, light is reflected through a range of different angles. This occurs on rough surfaces such as paper, corrugated glass or a painted wall. The surface of an ordinary paper may appear smooth, but if seen under a microscope, it will appear rough with many small protrusions.

Characteristics of the image formed in a plane mirror

a)    The image is virtual, that is, it cannot be captured on a screen.

b)    The image is as far behind the mirror as the object is in front of the mirror.

c)     The image is upright.

d)    The image is of the same size as the object.

e)    The image is laterally inverted i.e., left to right inversion.

Applications of Mirrors

a)    Two plane mirrors inclined at 450 are used in Periscopes, which enable a person to look over high walls and other obstacles.

b)    Plane mirrors are sometimes used in optical testing, where a person can read the inverted letters by seeing their images in a mirror. This helps in economizing the space in the testing room.

c)     Used in blind corners of the roads to help drivers see around these corners before making a turn.

d)    Used in certain meters below the pointer help us take proper readings without parallax error.

e)    Plane mirrors are also used in overhead projectors and telescopes.

Number of images formed on inclination of two plane mirrors

The number of images of a point object placed between two plane mirrors inclined at an angle θ,

N = (3600/θ) – 1

If 3600/θ is an even integer;

N = (3600/θ) – 1,

If 3600/θ is an odd integer and the object lies on the bisector of the angle θ then n = 3600/θ

When two plane mirrors are kept facing each other at an angle θ and an object is placed between them, multiple images of the object are formed as a result of multiple successive reflections.

When the two plane mirrors are placed parallel to each other, then

N = (360/zero) = (infinite number of images)


Reflection of Light overview  Reflection of Light overview Reviewed by knowledge people creators on November 21, 2021 Rating: 5
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