Reflection of Light
The object that emits light is called a light source. Light sources can be of two types—a material that emits light by itself is called a self-emitting source. Like the sun, stars, electric lamp, burning candle, etc. On the other hand, an object that has no light of its own but reflects light from a self-luminous object is called a non-luminous source. Most of the objects around us are inert. Moon and planets are also inert. We see them illuminated because they reflect sunlight.
Definition of Reflection of Light: When light passes through one medium and is incident on the surface of another medium, some of the incident light changes direction and returns to the first medium. This phenomenon is called reflection of light.
A Few Definition
M1M2 is a reflector (M1M2 can also be thought of as the interface between two media). A ray of light AO is incident on the reflector at point O and reflected along the path OB.
- Incident Ray: The light ray that is incident on the reflector is called the incident ray. AO is an incident ray.
- Reflected Ray: The light ray that is reflected from the reflector and returns to the first medium is called the reflected ray. OB is the reflected ray.
- Point of Incidence: The point at which a ray of light is incident on the reflector is called the point of incidence. Point O is a point of incidence.
- Angle of Incidence: The angle that the incident ray makes with the normal to the reflector at the point of incidence is called the angle of incidence. ∠AON is the angle of incidence (i).
- Angle of Reflection: The angle that the reflected ray makes with the normal drawn on the reflector at the point of incidence is called the angle of reflection. ∠BON is the angle of reflection (r).
Laws of Reflection
Reflection of light obeys the following two laws. These are called laws of reflection.
- The incident ray, the reflected ray, and the perpendicular drawn on the reflector at the point of incidence lie in the same plane.
- The angle of reflection is equal to the angle of incidence. That is, ∠BON = ∠AON.
Types of Reflection
Depending on the nature of the reflecting surface, reflection can be of two types:
- Regular Reflection, and
- Diffused Reflection.
Regular Reflection
If a bundle of parallel rays strikes a smooth plane reflector and is reflected as a bundle of parallel rays, then such reflection of light is called regular reflection. Mirrors, still water surfaces, smooth metal surfaces, etc. have regular reflections of light.
In the case of a smooth plane, the perpendiculars drawn on the reflecting plane at the point of incidence of the rays are parallel to each other. Therefore, in the case of regular reflection, if the incident rays are parallel to each other, then the reflected rays are also parallel to each other. An image of an object is formed only by regular reflection. So, in a plane mirror, we see our reflection.
Let us suppose that a beam of light from a source falls on a smooth reflecting surface. In this case, only that part of the reflecting surface from which the reflected rays are reflected and reaches the eye of a viewer is seen by that viewer as relatively bright (compared to other parts of the reflecting surface). That is, the viewer sees the reflection of the source in that part of the reflector plane.
Diffused Reflection
If a parallel beam is incident on an uneven reflector, the beam is no longer reflected as a parallel beam. Such reflection of light is called diffused reflection. Room walls, white paper, ground glass, movie screens, etc. are uneven. Hence, they cause diffused reflection.
In the case of uneven surfaces, the perpendiculars drawn on the reflecting surface at the point of incidence of the rays are not parallel to each other. Therefore, in the case of diffuse reflection, the incident rays are parallel to each other, but the reflected rays are not parallel to each other, i.e., are scattered. Diffuse reflection does not form any image of the object. So, we don’t see our reflection on the walls of the room.
Most of the objects around us we see are due to diffused reflections. A beam of light from a source falls on the uneven surface of the object and is scattered by diffused reflection. As a result, wherever the viewer is positioned, some reflected rays from almost all parts of the reflecting surface enter his eyes. So, he sees the object clearly. That is, in this case, the reflector appears fairly equally bright in all directions, and no reflection of the source is seen.
Deviation of a Ray due to Reflection
The angle by which a light ray deviates from its original path as a result of reflection is called the deviation of the ray.
Let us say that a ray of light AO is incident at point O on reflector M1M2 and is reflected in the path OB. At point O, the perpendicular to the reflecting plane is ON.
By law of reflection, ∠AON = ∠BON = i (assume)
Now, if the reflecting surface M1M2 were not present, the ray AO would have followed the path AOC. But due to reflection, the ray went in the path OB instead of OC, i.e., due to reflection, the ray is deflected.
The amount of this deviation, δ = ∠BOC = 180° – ∠AOB = 180° – 2i
Image of an Object
When light rays from an object fall directly into our eyes, we see the object at the point where it is located. But if the light rays from the object do not come directly but are reflected or refracted and reach our eyes, then we usually see the object elsewhere. But the object does not really change its place; that is, the object actually stays in its own place. What is seen in the new position is actually the reflection of the object.
Definition of Image: If a ray of light coming from a point is reflected or refracted and meets another point or appears to be diverging from another point, then the second point is called the image of the first point.
Image is of two types:
- Real Image, and
- Virtual Image.
Real Image
If the ray of light coming from a point is reflected or refracted and meets at another point, then that second point is called the real image of the first point.
Real Image can be Seen by Eye and Put on Screen: A real image is usually formed by a concave mirror and a convex lens. L is a point object in front of the lens. Rays from A fall on the lens and converge at point A’ after refraction. Hence A’ is the mirror image of A. If the screen is placed at point A’, the reflection of the object is seen on the screen. Images of movie screens, in-camera images, etc. are examples of real images.
Virtual Image
If a beam of light coming from a point is reflected or refracted and appears to be going away from another point, then that second point is called a virtual image of the first point.
A virtual image can only be seen by the eye but can’t be projected on the screen: A plane mirror forms a virtual image of an object. A point-effect in front of plane mirror M1M2. Rays AO, AC, and AD from A become divergent rays after reflection. The reflected rays are extended backward and converge at point A’. That is, the reflected rays from point A’ appear to be diverging. Hence A’ is the virtual image of A. Pond water creates a virtual image of pond plants. A mirage is also a virtual image.
FAQ about Reflection of Light!
What is the reflection of light?
- Reflection of light is the phenomenon where light bounces back from a surface instead of being absorbed. This is commonly observed when light hits smooth surfaces like mirrors.
What are the types of reflection?
- There are two main types of reflection: Specular Reflection (where light reflects off a smooth surface in a single direction, like on a mirror) and Diffuse Reflection (where light reflects off a rough surface and scatters in multiple directions).
What is the law of reflection?
- The law of reflection states that the angle of incidence (the angle at which light hits a surface) is equal to the angle of reflection (the angle at which light reflects off the surface).
What are the angle of incidence and angle of reflection?
- The angle of incidence is the angle between the incoming light ray and an imaginary line called the normal (perpendicular to the surface). The angle of reflection is the angle between the reflected ray and the normal.
Why is the angle of incidence equal to the angle of reflection?
- This equality is due to the nature of light and its behavior when it interacts with surfaces. It’s a fundamental property that stems from the symmetry of the reflection process.
Pingback: Refraction of Light: Detailed Guide on it
Pingback: Example of Reflection and Refraction of Light