Reflection of Light at plane surface - Part 1

Reflection of Light by Plane Mirror:

Def: The phenomenon of bouncing back of light rays in the same medium when they strike/incident on a smooth flat surface of an object.

Explanation: For mirrors, more than 95% of light may be reflected. Let us understand the concept of reflection from the given side diagram. Reflection of light is like bouncing back of a rubber ball after hitting a wall or any other hard surface.

A Plane Mirror is a flat mirror that is made up of glass and whose backside is coated with a very thin

layer of Silver.

From the side diagram, we can see that a ray PO is striking the polished surface (MM') of the mirror at point O and then bouncing back in the same medium through a ray OQ.

Here PO - Incident Ray, OQ - Reflected Ray, O - Point of Incidence, i - Angle of Incidence, r - Angle of Reflection, Normal - Perpendicular line dividing PO and OQ.

The above concept shows that the reflection of a light ray obeys the following two laws known as Laws of Reflection.

Laws of Reflection: 

The following are the TWO laws of reflection, they are:

1. Angle of Incidence (<i) is equal to angle of reflection (<r) i.e., <i=<r

2. The incident ray, reflected ray and the normal lies in a same plane.

Note: The above two laws of reflection are valid for all types of surfaces including spherical surfaces.

4 Characteristics of plane mirror:

1. The image formed by a plane mirror is virtual, erect and of the same size as that of the object.

2. In a plane mirror, object distance and image distance are same.

3. The size of image and object are equal.

4. The image formed is laterally inverted.

Uses of Plane Mirror:

1. Plane mirror is used as seeing/looking mirror in dressing table to see our own image.

2. It is used in the construction or making of periscope.

3. It is used in automobiles for various uses.

4. It is used in torch light.

5. It is used as shaving mirror.

Fundamentals of Light

What is Light?

Light is a form of energy, which induces the sensation of vision in our eyes and makes us able to see various things present in our surroundings. Under ordinary situations, light travels in a straight line. The straight line followed by light is called Light-ray.

The light ray may be the object's self light (luminous object) or reflected light (non-luminous object).

Luminous Objects: The objects which can emit light on their own. Eg., Sun, Bulb, Tubelight, etc.

Non-Luminous Objects: The objects which cannot emit light on their own. They reflect light from other sources. Eg., Moon, Painting, etc.

7 Most Important Properties of Light:

1. Reflection
2. Refraction
3. Dispersion
4. Scattering
5. Diffraction
6. Interference
7. Polarization

Nature/Characteristics of Light:

• Light is a form of energy

• It is an electromagnetic wave (EM wave)

• It propagates in a straight line

• It is a transverse wave that does not need any medium to travel. It can travel through a vacuum with a speed of 3×10⁸ m/s.

• The velocity of the lightwave changes from one medium to another medium during its propagation.

• The wavelength of light changes from one medium to another medium whereas its frequency remains the same in all the media.

Significance/Importance of Light:

Light may be classified as Natural Light and Artificial Light. In this era, especially human beings cannot imagine their life without light. Light plays an important role in the life all the living creatures present in our planet. 

Importance of Natural Light: Sunlight

• The significance of sunlight could be understand by the photosynthesis process takes place in plants. As plants synthesize nutrients from light and filter the air by consuming carbondioxide and releasing oxygen that we breathe. Hence everything depends on light.

• SunLight plays a key role in maintaining good health. The human being needs to be exposed to sunlight to regulate their body function properly. As we all
  
  
  know that sunlight contains Vitamin D which is necessary to human body.

• The lack of sunlight can cause disturbance in the form of Vitamin D deficiency, Calcium deficiency,  deregulate the release growth harmone. It can also impact the metabolism regulation and also cause fatigue and tiredness.

Importance of Artificial Light:

• Articial light helps in bringing energy to our home even in cloudy and rainy days, at night time.

• Artificial Lighting is very much essential and needful at home to create a pleasant atmosphere that helps to enjoy the life. During occasions light decoration enhances the beauty of that place.

• Now a days, wearing blue light glasses is getting popular as they reduces the risk of eye problems during the usage of smartphones and computers.

The relationship between Physics and Mathematics

The illustration and description of nature begin to be easy if we are free to use Mathematics. We try to get this point by seeing the following example:

To say that Force is equal to the product of the mass of the body and its acceleration, is somewhat lengthy and often difficult to say.

So, by using mathematical terms, we can say it as 

F=ma

Likewise, mathematical techniques such as Trigonometry, calculus, algebra, and geometry can be used to make predictions.

The role of mathematics in physics is to represent the laws in the form of equations and to obtain the conclusion or solutions referring to the observed conditions.

However, Mathematics is the language of physics. Failing to get the knowledge of mathematics leads to face difficulty in discovering, understanding, and explaining the laws of nature. The scope of mathematics in today’s era cannot be argued.

Anyhow, mathematics itself is not physics. We use language to express or convey our message. But the message we want to express has the main focus. If we are poor at the vocabulary and grammar of the language then it would be difficult for us to communicate and express our message.

From the 17^th century, the advancement in the study of mathematics seems to be motivated by the study of physics. A dedicated example of this can be calculus. The creation of calculus

and its enhancement in the concept is strongly related to physics. Newton also regarded Geometry to be a strong branch of Mechanics and the way we see it now; we can be sure that he was right at that time.

As time goes on, more mathematics came into existence and more of them started using physics.

The main goal of physics is to explain the relationship between various measurements of physical objects. A large portion of mathematics is devoted to comprehending and defining the relationships between objects. Therefore, the application of mathematics in physics is undeniable if you consider this aspect common in both subjects.

While learning the subject of physics, the relationship between mathematics and physics must be clearly understood and keep in mind throughout the learning journey of physics.

What is Physics?

When we start studying physics, so many questions raises, the first thing that comes to our mind is what is Physics? Why we study physics? Why physics is so-called a tough subject? What is its implementation in human life? If all the questions are answered properly then we develop an interest in the subject. 

What is Physics?

The word "Physics" is extracted from the Greek word whose meaning is Knowledge of Nature. It is a fundamental science with a wide number of concepts that explain the nature and working secrets of the universe. It explores the accurate description of the material universe. It also deals with matter and energy and their transformations.

Why study Physics?

Physics is a subject of adventurous exploration of universal secrets and their working process. It explains answers and their reasons to our exciting questions such as why the sky is blue, why the body with some mass reaches the ground when we throw it up, why the rainbow occurs, why the rainbow has colors, etc.

Is studying/learning Physics easy?

Studying Physics is challenging, sometimes difficult to understand the concepts but it is often a satisfying subject. Even though Physics gained a reputation as a very difficult subject, yet it is easy and simple if we understand some basic and fundamental laws. If you lodge these laws in your permanent memory then you can easily understand how the whole universe behaves in a variety of situations.

What are the implementations/uses of Physics in our Life?

Physics has an enormous number of applications. It includes:

1.Engineering and Communication

2. Medical Physics

3. Computers

4. Environmental Physics

5. Geophysics

6. Quantum mechanics

7. Theory of relativity                                                       

8. Material Science

It provides an explanation to the questions like why the stars are shining, how the planets revolve around the sun, and so on......