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Laws of Reflection

  • Last Updated : 05 Mar, 2021

The ability to see the surrounding objects depends upon the extent of light that enters our eyes after reflection from it. In more common terms, it is when the light from any object enters our eyes that we see it. The light is emitted by the object or reflected by it. Some of the important theories related to light are:

Light is that energy source that enables us to see. It is emitted from a source as the Sun. The word refers to the visible light, which is visible to the human eye and is responsible for the sense of sight of the object.

What allows us to see the objects?

Our eyes alone cannot allow us to see the object. The light from a source falls on the object and then bounces off onto our eyes from its surface and that is how we perceive it. Some objects are luminous that is they have a light of their own or somehow can produce light, and so they enable us to see them clearly. Some examples include the sun, matchstick, light lamp, stars, etc. Some emit light of their own and some by the use of electricity or any other thing.

On the contrary, there are some objects which do not emit light of their own and so are termed as non-luminous objects. Our eyes cannot see those objects clearly as the light from their surface is not reflected in our eyes. Some of the examples are trees, soil, grass, shoe, pencil, scale, etc.



Whenever light from any source is reflected it follows some laws which are listed below. It is because of this nature that we can perceive a better image of the object when viewed at a correct angle. The things which don’t reflect light are very hard to identify when we are in dark.

The amount of light that enters our eyes is regulated by the pupil of our eyes in which iris muscles play an important role in broadening the size of the pupil in a dark room so that more light can enter, and we can see properly and on the other hand decrease the size of the pupil when in a highly lighted room so that our eyes are protected from the over entrance of light.

Laws of Reflection

Reflection

The light gets reflected from the surfaces. Any surface which is polished or in other words is shiny always acts like a mirror. The observation of light bouncing off the surfaces is termed as reflection. The light after reflection travels in the same medium from where the ray was incident on the surface. The phenomenon of reflection doesn’t change the velocity of light it only reverses the direction of light incident on it. This can be observed on any surface which is rough or smooth. The path of the reflected ray will depend upon the extent of smoothness of the surface, in the case of smooth surface the reflected ray emerges with the same angle as of incidence and in the latter case suffers irregular reflection and so the reflected ray doesn’t emerge same as that of incidence angle.

Following are the “Laws of reflection”

  • The ray of light that falls on a reflecting surface is known as the incident ray and the ray that is reflected back is known as the reflected ray.
  • An imaginary line that is perpendicular to the reflecting surface from where the reflection occurs is known as the normal.
  • The angle of incidence ∠i refers to the angle between the incident rays with the normal. The angle of reflection ∠r refers to the angle between the reflected rays with the normal.

Laws of Reflection

  1. The Angle of incidence ∠i is always equal to the angle of reflection ∠r (∠i =∠r).
  2. The incident ray at the surface of the polished surface, the reflected ray, and the normal which is at the point of incidence, all lie in the same plane.

Reflection through Plane Mirror

A plane mirror refers to a mirror with a flat (planar) reflective surface. The light rays when striking a plane mirror, the angle of reflection equals the angle of incidence always. The angle of the incidence refers to the angle between the incident ray and the surface normal (an imaginary line perpendicular drawn to the surface). In a similar way, the angle of reflection is the angle between the reflected ray and the normal at the point of incidence.

Characteristics of image formed by plane mirror:

  • The image formed is exactly of the same size as the object.
  • The position of the image beyond the mirror is the same as that of the object in front.
  • The image formed is virtual.
  • The plane mirror always forms a real image of the object.
  • The image obtained in the plane mirror is always erect.
  • The phenomenon of lateral inversion can be observed. Where the right appears to be left and vice versa.
  • If we stand in front of the mirror the image will be of the same size, height, virtual, erect, and laterally inverted.



Concave and convex mirrors are some of the widely used mirrors which come under the spherical mirrors, can produce virtual images of an object similar to a plane mirror. On the contrary side, the images formed by them are not always of the same size as the object like in the case of a plane mirror. The image by a convex mirror, the virtual image formed is always diminished in size, however in the case of a concave mirror when the object is placed somewhere between the focus and the pole of the mirror, an enlarged virtual image can be seen. However, when we need a virtual image of the same size a plane mirror is preferred over spherical mirrors.

Sample Questions

Question 1. If the angle of incidence is 30 degrees then find the angle between normal and surface.

Answer:

Angle between surface and normal is always equal to 90 degree.

Question 2. What will be the angle of reflection for the incident angle 45°?

Answer:

We know that,

∠ i = ∠ r

Therefore, ∠r = 45°



Hence, the angle of reflection will be 45°

Question 3. What will be the angle of incidence for the reflected angle 40°?

Answer:

We know that,

∠ i = ∠ r

Therefore, ∠i = 40°

Hence, the angle of incidence will be 40°

Question 4. What will be the incident angle if the angle between the mirror surface and the incident ray is 50°?

Answer:

We know that,

∠i + angle between mirror and incident ray = 90°

Therefore, ∠i + 50° = 90°

Therefore, ∠i = 90° – 50°

Therefore, ∠i = 40°

Hence, the incident angle is 40°

Attention reader! Don’t stop learning now. Participate in the Scholorship Test for First-Step-to-DSA Course for Class 9 to 12 students.

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