Introduction: We see so many objects around us, colourful and different. We see things like buses, cars, cycles, trees, animals, and sometimes flowers on the way to school. Do you ever think, how do we see all these objects? Again, think of the same places at nighttime if it were completely dark. What will you see? You will see nothing because there is no light there. But, when you light a candle or a torch, you can see the objects present there. Without light, things can not be seen.

Light helps us to see objects. Have you noticed, when you hold an opaque object in the source of light, you get a dark patch formed behind the object? This is its shadow. Do you know when light is incident on a shiny surface, it gets reflected or bounces back. In this article, we will learn about light, shadow, and reflections. We will also discuss the behaviour of light on different objects, the formation of shadow, and how the light gets reflected.

Light

Light is a form of energy. To make the objects visible, we need a light source. During the day, Sunlight allows us to see things. Artificial light makes us see objects in the darkness. We can see an object when a light comes from it or when it is reflected from it. We detect light with our eyes.

Study Prism and Dispersion of Light

Sources of Light

Source of light are those objects which give out light. Some light sources around us are Sun, stars, tube lights, kerosene oil, petroleum gas, candle, torch, etc. The most important source of light for us is the Sun. The distance of the Sun from us is about \(150\;{\rm{million}}\;{\rm{km}}\), but its light makes the daytime bright on the earth. But at night, we use an electric bulb, tube light, lamp, candle, or torch as a light source.

Luminous & Non-luminous Objects

1. Objects like the Sun that give out or emit light of their own are called luminous objects.
   E.g. Bulb, Sun, and other stars.
2. Objects that do not produce their light but reflect the light emitted by luminous objects are known as non-luminous objects.
   E.g. Earth, moon, trees, etc.

Transparent, Opaque and Translucent Objects

Based on interaction with light, we can classify objects as:

1. Opaque: When a ray of light falls on opaque objects, it does not allow light to pass through them, so we cannot see through it.
   E.g. Stone, metal, wood.
2. Transparent: If you can see clearly through an object, it allows light to pass through it and is transparent.
   E.g. Clean glass, water, air, etc.
3. Translucent: When a ray of light falls on transparent objects, it allows light to pass through them, and we can see through it
   E.g. Wax paper, frosted glass, butter paper, smoke, etc.

Light Travels in a Straight Line

When we shine a torch at night, we will see that the beam of light produced by the torch travel straight into darkness. The beam of searchlight at the airport shows that light travels in straight lines. The formation of shadow by a source of light also suggested that the light travels in a straight line. This happens because no shadow could have been formed if light could bend and travel in curved lines.

After all, the light would have reached behind the object. Hence we can say that light travels in a straight line, and this property of light is called rectilinear propagation of light.

Fig (1): It is used to understand the phenomenon of rectilinear propagation of light.

Shadow

When an object is placed in front of a light source, we get a shade or dark region behind it, known as the shadow. Shadows are formed when an object stops light. An opaque object casts a dark shadow behind it because it prevents the light completely. A translucent object casts a weak shadow because it stops the light partially. A transparent object does not cause any shadow behind it because a transparent object does not stop any light from passing through it.

For example, the ceiling fan’s shadow hung in the centre of the room will fall on the side opposite the lighted electric bulb. A lighted candle fixed in a room will also cast our shadow and the ceiling fan on the opposite side. If we stand in Sunlight, our body casts a shadow on the ground. And when we walk in Sunlight, our shadows always walk with us.

Fig (2): Some examples of shadow.

To observe a shadow, we require these three things that are :

1. A source of light
2. An opaque object
3. A screen on which the shadow can be seen

Shadow Formation

1. When an opaque object comes in the path of light, then a shadow is formed.
2. When a shadow is formed, it needs a screen where it is formed, for example, the ground, walls of a room or any surface.
3. We get an idea about the shapes of different objects from the shadow, but sometimes they mislead us.

A Pinhole Camera

It is the simplest kind of camera without any lens. It uses a tiny opening to focus all light rays within the smallest possible area to obtain an image as clearly as possible. We always get an inverted image using a pinhole camera.

Image Formation by a Pinhole Camera

1. A pinhole camera consists of a light-proof box, a thin film for a screen, and a small aperture or hole to allow the passage of light rays.
2. It forms an image on the inverted screen when the light from outside enters through the small hole through it.

Pinhole Camera Image Characteristics

1. We can obtain a real image on the screen.
2. The size of the image obtained is comparatively smaller than the actual object.
3. The image formed is inverted on the \(x-\)axis as well as on the \(y-\)axis.

Mirrors and Reflection

A mirror usually consists of glass. When a light incident on it, it get reflected and forms clear erect images. We all use mirrors at home. When you look into the mirror, it reflects your face in the mirror. We can also see reflections in the water of a pond or a lake, trees, buildings, and other objects.

When light is incident on any well-polished surface or shiny acts like a mirror, it gets reflected or bounces back in the same medium as shown in the below figure. This phenomenon of light is called reflection.

Fig (3): The reflection of light

Characteristics of Image

1. When rays of light that come after reflecting from objects converge, and then the image is formed. Images have colour, unlike shadows.
2. The actual convergence of light rays forms a real image, and it is formed on the screen.
3. A virtual image cannot be obtained on a screen because it is the apparent convergence of diverging light rays.

Laws of Reflection

The laws of reflection are given following:

1. The angle of incidence is equal to the angle of reflection.
2. The incident ray, the reflected ray, and the normal at the point of incidence all lie in the same plane.

Summary

When a ray of light falls on opaque objects, it does not allow light to pass through them, so we cannot see through it. When a ray of light falls on transparent objects, it allows light to pass through them, and we can see through it. In translucent objects, it allows light to pass through them partially. We get a shadow when we put an opaque object in the path of light.

A pinhole camera can image the Sun and brightly lit objects. It can be made with simple materials. Mirror reflection gives us clear images. Images are very different from shadows. Light travels in a straight line.

Learn Concepts on Reflection of Lights

FAQs

Q.1. What is the difference between a luminous and a non-luminous body?
Ans: Luminous bodies are the bodies that emit light. For example, Sun, stars, burning candles, etc., and non-luminous bodies are those bodies that do not emit light. For instance, moon, earth, and blackboard.

Q.2. What are the necessary conditions for the formation of shadow?
Ans: The necessary conditions for the formation of shadow are given below:
(1) There should be an opaque material.
(2) A source of light and screen should be available.
Then a shadow is formed on the screen when the object is placed in the path of light.

Q.3. Define reflection of light.
Ans: Light rays, after striking the smooth and shiny surface, get reflected or bounce back; this phenomenon of light bouncing off surfaces is called reflection.

Q.4. What do you mean by scattering of light?
Ans: When a beam of light incident on a rough surface, this light turned back in different directions. This phenomenon of light is known as the scattering of light.

Q.5. Have you ever seen an ambulance? Why is an ambulance written in the form of a mirror image on vehicles?
Ans: It is written as a mirror image on vehicles so that people can see in their rearview mirrors, read it correctly and immediately give way to the vehicle as it carries patients who need urgent medication.

We hope this detailed article on lights, shadows, and reflection helped you in your studies. If you have any doubts, queries or suggestions regarding this article, feel to ask us in the comment section and we will be more than happy to assist you. Happy learning!