     # Reflection Of Light by Plane Mirror ... Diffused/Irregular reflection is a non-mirror-like reflection

• View
0

0

Embed Size (px)

### Text of Reflection Of Light by Plane Mirror ... Diffused/Irregular reflection is a non-mirror-like...

• Reflection Of Light by Plane Mirror

Let us do a quick activity before we move ahead with the lesson.

Close your eyes for 10 seconds and count to 10; now when you open

your eyes again, what do you observe? Do you observe all the things

around you? What are the phenomena that allow you to see things

around you? Does the phenomena Reflection of Light have anything

to do with this? Let us know more about it.

What is Reflection of Light?

When a ray of light falls on any object (polished, smooth, shiny

object), light from the object bounces back those rays of light to our

eyes and this phenomenon is known as “Reflection” or “Reflection of

Light”.

This phenomenon is what enables us to look at the world around us

and is based on the property that light travels in a straight line. For

example, twinkling of stars or light reflected by a mirror.

• ​ (Source: Wikipedia)

Laws of Reflection

In the diagram given above, the ray of light that approaches the mirror

is known as “Incident Ray”. The ray that leaves the mirror is known as

“Reflected Ray”.

• At the point of incidence where the incident ray strikes the mirror, a

perpendicular line is drawn known as the “Normal”. This normal is

what divides the incident ray and the reflected ray equally and gives

us the “Angle of Incidence” (Qi) and “Angle of Reflection” (Qr).

Hence the above information gives us the “Laws of Reflection of

Light” which state that :

a. The angle of incidence is equal to the angle of reflection.

b. The incident ray, the normal and the reflected ray, all lie in the same

plane.

Types of Reflection :

There are majorly two types of reflection :

a. Specular/ Regular reflection

b. Diffused/ Irregular reflection

a. Specular/Regular reflection :

https://www.toppr.com/guides/physics/ray-optics-and-optical-instruments/reflection-of-light-by-spherical-mirrors/

• Specular/Regular reflection is a mirror-like reflection of rays of light.

Here the rays of light which are reflected from a smooth and shiny

object such as a mirror, are reflected at a definitive angle and each

incident ray which is reflected along with the reflected ray has the

same angle to the normal as the incident ray. Thus, this type of

phenomena causes the formation of an image.

​(Source: Wikipedia)

Learn ​how is Image formed in Spherical Mirror here​.

b. Diffused/Irregular reflection:

https://www.toppr.com/guides/physics/light-reflection-and-refraction/image-formation-by-spherical-mirrors/

• Diffused/Irregular reflection is a non-mirror-like reflection of light. In

this type of reflection rays of light that hit an irregular object with a

rough surface, are reflected back in all directions. Here, the incident

ray which is reflected along with reflected ray doesn’t have the same

angle to the normal as the incident ray.

Thus, this type of reflection doesn’t form an image.

(Source: Wikipedia)

Image Formation by a Plane Mirror

• Let us take a mirror MM’ as shown in the diagram given above. Let us

suppose an object AB of size ‘h’ on the left-hand side of the mirror at

a distance ‘u’.

• An incident ray of light AP from point A of the object AB falls on the

mirror MM’ at point P. This incident ray AP is reflected back in the

same path PA. Another ray OC falls on the mirror MM’ at a point O

and is reflected along the path OC. Now, since reflected rays PA and

OC are diverging and therefore cannot meet each other in front of the

mirror, hence we extend these rays PA and OC behind the mirror by

dotted lines. On extending these rays behind the mirror, we see that

these rays meet at point A’ at a distance V’. Therefore A’ is the virtual

image of point A of the object AB.

Similarly, a virtual image of point B will be formed behind the mirror

as B’ from the incident rays BO and BE.

Now, to get a complete image of the object AB, we join the point A

and B to point A’ and B’ by a dotted line. In doing so, we find that the

image A’B’ being formed is virtual, erect and of same shape and size

as the object AB; thereby giving us the characteristics of images

formed by the plane mirror.

Characteristics of Images formed by Plane Mirror

https://www.toppr.com/guides/physics/light/reflection-of-light/

• a. Images formed by a plane mirror are “Always Virtual”.

b. Images formed by a plane mirror are “Erect/Upright”.

c. Images formed by a plane mirror are of “same shape and size” as

that of an object.

Solved Example for You

Q. A ray of light strikes a reflective plane surface at an angle of 42​o

with the surface.

a. Find the angle of incidence.

b. Find the angle of reflection.

c. Find the angle made by the reflected ray and the surface.

d. Find the angle made by the incident and reflected rays.

Sol: We’ll use a diagram given below to answer the question:

• a. Angle of Incidence (Q​i​)= 90​0​-42​0​= 48​0

b. Angle of Reflection (Q​r​)= (Q​i​)= 48​0

c. x = 90​0​-Q​r​ = 90​0​-48​0​ = 42​0

d. Q​i​ + Q​r​ = 48​0​ + 48​0​ = 96​0

Terms Related to Spherical Mirrors

“Mirror, mirror on the wall, who’s the fairest of them all?” We’ve all

heard this dialogue from the story of Snow white and the seven

dwarfs. But what kind of mirror was it? What were the properties that

enabled these spherical mirrors to be so special? Well, let us find

answers to it in this section.

• There’re few basic and important terms one needs to know while

studying spherical mirrors inside the chapter “Reflection and

Refraction”:

a. Center of Curvature (c)

c. Pole (p)

d. Principal axis

e. Aperture

f. Principal Focus or Focal Length

g. Focus

a. Center of Curvature (c) :

• (Source: Wikipedia)

The Center of Curvature of a spherical mirror is the point in the centre

of the mirror which passes through the curve of the mirror and has the

same tangent and curvature at that point. It is denoted by the letter ‘c’.

It’s the linear distance between Pole and the Center of curvature.

c. Pole (p) :

It’s the midpoint of the spherical mirror.

d. Principal axis:

• It’s an imaginary line passing through the optical centre and the centre

of curvature of any lens or a spherical mirror.

e. Aperture:

An aperture of a mirror or lens is a point from which the reflection of

light actually happens. It also gives the size of the mirror.

f. Principal Focus :

Principal Focus can also be called as Focal Point. It’s on the​ axis​ of a mirror or lens wherein rays of light parallel to the axis converge or appear to converge after reflection or refraction.

Principal Focus is also what determines the Focal Length of the mirror.

g. Focus:

It’s any given point, where light rays parallel to the principal axis, will

converge after getting reflected from the mirror.

What is an Image?

When an object is placed in front of a mirror, we see an image of the

object placed. This image appears to be behind the mirror, and is

called “Image”. The object is the source from which incident ray

occurs and the image that is formed is because of the reflected rays.

The image formed maybe “Real” or “Virtual”.

• Wherein the “real” image is formed when the light rays from the

object actually intersect each other after reflection. Real images are

formed inverted and can be projected on to a screen. On the other

hand, a “virtual” image is formed when the light rays from the object

don’t actually intersect each other after reflection. Although they

“appear” to do so when they’re produced behind the mirror. Virtual

images are “always” erect and cannot be projected on a screen.

Concave and Convex Mirrors. ​(Source: Wikipedia)

See how Image is formed by Spherical Mirrors here

Types of Spherical Mirrors

https://www.toppr.com/guides/physics/light-reflection-and-refraction/image-formation-by-spherical-mirrors/

• Spherical mirrors are of two types:

a. Concave Mirror

b. Convex Mirror

detail here​.

a. Concave Mirror

A con

Recommended ##### Collaborative Reflection Insights from the MIRROR project presented @ CSCL 2013
Education ##### Christian Object Lesson - God’s Word – a Mirror for Reflection
Spiritual ##### COST EFFECTIVE PV SOLAR ENERGY CONCENTRATING SYSTEM BASED ON MIRROR REFLECTION
Documents ##### Mirror Reflection in Experiential Learning Travus Burton, Experiential Learning Coordinator. Why Reflect?
Documents ##### Telescopes. Images can be formed through reflection (mirror) or refraction (lens). Reflecting mirror Optical Telescopes
Documents ##### Investigation 20B: Reflection in a plane mirror Web view Investigation 20B: Reflection in a plane mirror
Documents ##### Mirror, mirror on the wall: Building a new PHP reflection library (DPC 2016)
Technology Documents