Well, waves is a very common word. Every one of us has heard it. And to be on the same page, we are talking about waves such as electromagnetic waves, light waves, sound waves, etc. These are some of the waves that are a part of the class 10 physics courses. Attached to this, there are many other topics in the course like magnetism, kinematics, laws of motion and atomic structure of matter.

Here in this article, we will take a brief look into various types of waves that are included in the class 10 physics course. The sound waves are exactly not a part of the class 10 syllabus but we will also discuss a bit about that also. The major focus of our article would be on the light wave only. It is known that light behaves as a wave apart from being just a particle form. So, let’s unravel the various concepts of light waves.

A comprehensive look into the concepts of the light wave in basic physics

Well, have u ever wondered why something in front of you is visible to you. Light is that magical thing that makes everything in front of you visible to you so easily. And to take a closer look at this, let us study the concept of a light wave.

It was thought earlier that light travels in the form of rays as the shadow of objects were easily cast on the surfaces. But, later it was found that if the object in the way of light becomes extremely small, light tends to bend around it. This phenomenon is called the diffraction of light. Though it is not a part of the course, it is just to enhance your knowledge. So, anyway, the phenomenon of diffraction raised questions regarding the ray nature of light. For this, the light was called as a wave.

Until the modern quantum theory declared that light has particle characteristics with a wave nature. Hence, we will study various concepts of light in further sections.

Phenomena of Reflection

Class 10 physics light reflection
Light-reflecting from the water surface, Source: Pixabay

Now, just like a ball comes back after hitting the wall, the light also does the same. The only difference is that light comes faster. This phenomenon of bouncing back of lightwave after hitting a polished surface like a mirror is known as reflection. Though, there are some laws to this phenomenon. 

The two basic laws of reflection are:

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

Now, when lightwave falls on a plane mirror, the image created by the mirror is laterally inverted along with being virtual and erect. The next section will deal with spherical mirrors and images created by them. We will also understand the mathematical expressions of these surfaces.

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Spherical Mirrors

Talking about spherical mirrors, they are of two types. The one with the reflecting surface curved inwards and the one with curved outwards. The mirror that has its reflecting surface curved inwards is called a concave mirror whereas the one with the reflecting surface curved outwards is called a convex mirror.

If we move further with the study of image formation by these mirrors. The image formed by a convex mirror is always virtual and erect, though there can be variation in the size of the image based on the position of the object.

On the other hand, the concave mirror forms a real and inverted image. As long as the object is at infinity, focus or in between them. If in case, it is between focus and pole the image will be virtual and erect.

You can also find a proper ray diagram of all the cases of convex and concave mirrors. Also, we can derive mirror formulas. The one for spherical mirrors is: 

1/v + 1/u = 1/f where 

u is the object distance, 

v is the image distance, and 

f is the focal length of the mirror.

Phenomena of refraction of lightwave

Class 10 physics
A refracted image through a glass, Source: Freepik, Credits: BRGFX

Among the various popular topics of physics like the concept of electromagnetism, particle physics, special relativity, and gravitation. The refraction of light has a special place. Now, why does a coin in the bucket full of water appears to be raised? The phenomenon that makes it possible is known as the refraction of light. Refer to this link for learning particle model in class 10 physics.

Unlike reflection, refraction deals with bending of light when it passes from mediums with the varying refractive index. Now, the medium with a refractive index more than the other one is the denser medium, whereas the medium with a low refractive index is the rarer. When the light goes from a rarer to denser medium, it gets refracted and bends towards the normal. When the light travels from denser to rarer medium, it bends away from the normal. 

The normal is a perpendicular line drawn on the line of contact of the two mediums. To make it more clear, you need to refer to the rectangular slab diagram in the book. Just like reflection, refraction also has some laws:

  • The incident ray, the refracted ray and the normal to the interface of two transparent media at the point of incidence, all lie in the same plane. 
  • The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant, for the light of a given color and for the given pair of media. This law is also known as Snell’s law of refraction.

The term sine is used in trigonometry which you will learn in maths. It is necessary for light to follow these laws of refraction.

Talking about the refractive index, the general formula is:

n = Speed of light in medium 1/ Speed of light in medium 2, will give you the refractive index of medium 2 w.r.t medium 1.

Spherical Lenses

Camera convex lens, Source: Unsplash, Credits: Bernard

Now, as we are well versed with the concept of reflection and refraction along with mirrors. Let us switch to the spherical mirrors section. Just like the mirrors, spherical lenses are also classified as concave and convex.

A transparent material that is bounded by two curved surfaces is known as a lens. The one that has two surfaces bulging outside is known as a convex lens. On the other hand, the lens that has both the spherical surfaces bulging inside is called as the concave lens.

Just like mirrors, lenses also reflect and refract light. We will take a look at the image formation of the lenses in the next section.

Mirrors form images by reflecting light whereas the lenses form images by refracting light. There are many parameters that govern the refraction of light. They will be highlighted in the higher classes of yours, for now, let’s take a look at the image formation by lenses. We will also study the lens formulas here.

Just like the mirrors, the point of object placement is at infinity, focus, 2x focus, between them and between optical center and focus. The difference here is that the image is not formed on the same side of the lens in all cases. It is formed on the other side of the lens due to refraction. As the object distance from the lens becomes smaller, the size of the image becomes bigger. The image formed is always real and inverted except when the object is in between focus and optical center of the lens. This is in the case of a convex lens.

In the case of a concave lens, the image formed is always virtual and erect. It is always diminished. You can refer to the NCERT book of class 10 science to get a pictorial representation of these lenses.

The lens formula is as follows:

1/v - 1/u = 1/f where

u is the object distance

v is the image distance and,

f is the focal length of the lens

One can easily calculate the power of a lens by inversing the focal length as:

P = 1/f

This is all about the light wave topic in the class 10 physics, and to learn all the tips and tricks of light waves. You need to get in touch with a professional tutor. Or you can refer to some sample papers for practice.  Learn about the electricity chapter in class 10 physics  and various sources of energy here!

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