Light - Class 7 Science - New St. Mery English School

Light is a form of energy that enables us to see the beautiful world around us. Without light, everything would appear dark and invisible. The Sun is the main natural source of light for the Earth, while electric bulbs, candles, and tube lights are artificial sources of light.

Light travels in a straight line and helps us understand important concepts like reflection, shadows, and images formed by mirrors. When light falls on an object, it may be reflected, absorbed, or pass through it. This is why some objects are transparent, some are translucent, and others are opaque.

In this chapter, we will learn about sources of light, reflection of light, mirrors, and how light helps us see objects clearly. Let us explore the amazing properties of light and understand how it plays an important role in our daily life.

Light - Class 7 Science - New St. Mery English School

What is Light ?

Ans:- Light is the form of electromagnetic energy that makes everything visible. It can detected by human eyes.

What is rectilinear propagation of light?

Ans:- When light moves from one place to another, it follows a straight path as long as it travels through the same medium. This property of light is known as rectilinear propagation of light.

Ex:- When you switch on a torch in a dark room, the beam of light goes straight. You can see a straight line of light — that shows rectilinear propagation.

🌑 Shadow Formation

Shadows are formed because light travels in straight lines.
If an object comes in the path of light, it blocks the light and a shadow forms behind it.
Rectilinear propagation of light happens only when light travels in a uniform medium. When it changes medium (like air to water), it bends. That bending is called refraction.
Write an experiment that show that light travel in straight path

🎯 Aim
To prove that light travels in a straight path.
🧰 Materials Required

3 pieces of cardboard

A candle

Matchbox

A table

🛠 Procedure

Take three cardboards of the same size.

Make a small hole at the center of each cardboard.

Fix the three cardboards vertically on a table in such a way that the holes are at the same height.

Place the cardboards in a straight line, one behind the other.

Put a lighted candle behind the first cardboard.

Look through the hole of the third cardboard from the other side.

👀 Observation

When all three holes are in one straight line, the flame of the candle is clearly visible.

If you move any one cardboard slightly to the side, the candle flame cannot be seen.

🧠 Conclusion

This experiment shows that light travels in a straight line. When the holes are aligned, light passes straight through them. When the path is disturbed, light cannot bend around the cardboard to reach the eye.
Reflection of light
When light hits an object like a mirror, it does not pass through. Instead, it returns back into the same medium. This is called reflection of light.
Types of Reflection
There are two types of reflection of light
1- Regular Reflection
2- Irregular Reflection
Regular Reflection
Regular reflection happens when light rays fall on a smooth, polished surface and reflect in an orderly, parallel way. In regular reflection parallel rays of light hit a smooth surface and the reflected rays also remain parallel.
Ex:- A plane mirror gives regular reflection. That’s why you can see a clear image of yourself in it.
Irregular Reflection
Irregular reflection happens when light falls on a rough surface and reflects in many different directions. In irregular reflection parallel rays of light hit a rough surface and the reflected rays scatter in different directions.
Ex:- When light strike on a wall it gives Irregular reflection, Reflection of light in water
ray of light?
Ans:- A ray of light is a narrow stream (प्रबहित होना ) of light that represents the path along which light energy travels in a medium is called ray of light. it is represented by a straight line and an arrow marked on it. the arrow represents the direction of ray of light
beam of light?
Ans:- A group of light rays is called beam of light.
types of beam of light?
Ans:- There are three types of beam of light.
           1- Parallel beam of light
           2- Convergent beam of light
           3 - Divergent beam of light
Parallel beam of light?
Ans:- When the rays of light travel parallel to each other then the collection of such rays is called parallel beam of light .
convergent beam of light?
Ans:- When the rays of light coming from the different directions and meat at a specific point then the collection of such rays is called convergent beam of light.
divergent beam of light?
Ans:- When the rays of light emerge from a point source of light and travel in different direction , such beam of light is called divergent beam of light.

What is incident ray?
Ans:- A ray of light that is coming from source of light towards the reflecting surface is called incident ray of light.

What is reflecting ray?
Ans:- A ray of light bouncing away from the reflecting surface after reflection is called reflecting ray.

What is point of incident?
Ans:- The point on a reflecting surface where incident ray, reflecting ray and normal meet together is called point of incident.

What is normal?
Ans:- A line drawn perpendicular to the reflecting surface is called normal.

What is incidence angle?
Ans:- An angle which is formed between incident ray and normal is called incidence angle. It is represented by ' i '
Incidence angle = ∠i

What is reflected angle?
Ans:- An angle which is formed between normal and reflected ray is called reflected angle. It is represented by ' r '.
Reflected angle = ∠r

What are the 2 Laws of reflection of light?
Ans:- The two laws of reflection are
1- The incident ray, the normal at the point of incidence and the reflected ray all lie in the same plane.
2-The angle of incidence is equal to the angle of reflection. , ∠i = ∠r .

Image

An image is the picture of an object formed when light rays coming from the object reflect from a mirror or refract through a lens and reach our eyes.
Real image
The image that can be obtained on a screen is called real image
Virtual image
The image that can not be obtained on a screen is called virtual image
What is mirror?
Ans:- Any smooth polished surface which can turn the rays of light back into the same medium is called mirror.
Ex:- looking glass, highly polished metal, still water, still oil etc
How many types of mirror?
Ans:- There are two types of mirror.
1- Plane Mirror
2- Spherical Mirror
What is Plane Mirror?
Ans:- A plane mirror is a flat and smooth surface that reflects light to form an image. A plane mirror forms an image that is virtual, erect, Laterally inverted and Same size of the object.