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1. Concave mirror

2. pole

3. Smaller, virtual and erect

4. Concave mirror

5. 45°

6. infinite

Correct answer is (b) 1.33

Medium M₁ with refractive index 1.71 is optically denser than the other medium M₂. Speed of light decreases when it travels from rarer to denser medium.

Refraction of light rays, as they travel from one medium to another medium, obeys two laws,Which are known as Snell's laws of refraction .

They are :

1. The incident ray, the refracted ray and the normal at the point of intersection, all lie in the same plane.

2. The ratio of the sine of the angle of incidence (i) to the sine of the angle of refraciton (r) is equal to the refractive index of the medium, which is a constant.

\(\frac{sin\,i}{sin\, r}\) = μ

Refractive index of water = n_w = 1.33 

Refractive index of kerosene = n_k = 1.44 

∴ Refractive index of kerosene with respect to water is

 = \(\frac { { n }_{ k } }{ { n }_{ w } }\)

= \(\frac { 1.44 }{ 1.33 }\)

= 1.082

It is a convex lens.
No, when the object is placed close to a convex lens then the image formed is virtual which cannot be obtained on screen.

The table gives at a glance the position, size and nature of the image formed by a convex lens corresponding to the different positions of the object and also its application.

1. Take a silver paper used for decoration. 

2. Paste the silver paper without folds on a postcard size chart paper. 

3. Allow it to dry by keeping it under some heavy books 

4. Bend the sheet slightly forward as its shiny surface comes inwards. 

5. It works as a concave mirror. 

6. Now bend the sheet slightly backward as its shiny surface comes out wards.

7. It works as a convex mirror.

1. How the shining surface of the mirrors are bent? 

2. What do we call the mirror, if it has reflecting surface bent inwards? 

3. What do we call the mirror, if it has reflecting surface bent outwards? 

4. How is your image in the both the mirrors? 

5. Which mirror forms smaller image? 

6. Which mirror can form your image on the wall?

We can find irregular reflections on unpolished marbles floors, scratched steel vessels, broken mobile screens, disturbed water surfaces, and on the rough surfaces of plastic sheets, metal sheets, etc.

Concave mirrors are used by dentists, ophthalmologists, ENT doctors and also in head lights of vehicles. Convex mirrors are used as rear view mirrors in vehicles and safety mirrors at curved roads.

Applications of concave mirrors:

1. Concave mirrors are used by ENT doctors as Head Mirrors. 

2. Dentists also use concave mirrors to get a bigger image of the teeth. 

3. Eye specialist using a special instrument called Ophthalmoscope. It is fitted with a concave mirror having a small hole near its center.

4. Concave mirrors are used to reflectors in a torch light or the headlights of vehicles. 

5. These are used in microscopes.

Applications of convex mirrors:

1. Convex mirrors are used as Rearview mirrors in vehicles. 

2. Convex mirrors are also used at the junctions of roads. 

3. Convex mirrors are used at ATM machines. 

4. Convex mirrors are used for security purpose at factories, offices, etc.

(c) Radius of curvature

(c) Principal axis

(b) Centre of curvature

1) Light is a form of energy. 

2) Light energy releases from different objects called sources of light. 

3) Sources which release light energy on their own are called natural sources. 

Ex: sun, stars. 

Sources which need the human involvement to release light energy are called manmade sources of light. 

Ex: torch light, candle, bulb etc. 

4) Actually, light is not a single ray, but a bundle of rays. This bundle of light rays are called beam of light rays. 

These are three types : 

i. Parallel beam of light rays : 

Light rays which travel parallel to each other are called Parallel beam of light rays. 

ii. Converging beam of light rays : 

“Light rays which travel from different directions to meet at a point are called as Converging beam of light rays”. 

iii. Diverging beam of light rays : 

“Light rays which travel from a source moving in different’ directions are called as Diverging beam of light rays.”

1. The process of bouncing back of light rays into the same medium after falling on a smooth or rough surface from the light source is called “reflection of light”. 

2. When light falls on an object it reflects back. Reflected ray when reaches to our eyes, causes sensation of vision. 

3. If there is no phenomenon of reflection, we cannot see the colourful world. 

4. Periscope is prepared based, on the principle of reflection of light from plane mirrors. 

5. Kaleidoscope is prepared based on the principle of multiple reflection of light from plane mirrors. 

6. The dentists, ophthalmologists, ENT doctors etc. give us treatment by using reflection of light through the concave mirrors. 

7. The drivers of the vehicles observe the rear objects of his vehicles by using reflection of light through the convex mirrors. 

8. Hence, I appreciate the role of the reflection of light in our daily life.

The bouncing back of light when it falls on smooth surface is called reflection.

1. Light plays an important role in the sensation of vision. 

2. Now a day’s people, due to the usage of modern gadgets, like mobile phone, computers, televisions through which light enters the eyes. 

3. Watching TV too much or sitting very close to it may make your eyes-tired cause dryness of eyes and gradually lead to headache. 

4. While using computer or TV ensures that your room is well lighted. 

5. While watching TV or computer a simple rule 20 – 20 – 20 helps us in protecting eyesight. 

6. After 20 minutes of watching TV or computer screen, take 20 seconds break and watch the TV or computer around 20 feet away. 

7. Reduce blue light in cell phones and computers are switched on power saving mode during night. 

8. Yellow light has been proven effective in protecting retina than blue light which causes damage to retina.

Given : 

Radius of curvature = 25 cm

To find: F = ?

f = \(\frac{R}{2}\) = \(\frac{25}{2}\)

f = 12.5 cm

(A) Regular reflection of light takes place.

When a ray of light fall on a surface and angle of incidence is equal to the angle of reflection (law of reflection hold true) we called regular reflection.
In case of polished wooden table law of reflection hold true because the surface is polished (smooth). Thus there will be a regular reflection.

(B) Diffuse reflection of light takes place.

When a ray of light fall (strike) on the surface of Chalk powder, reflected ray get scatted in a different direction with a different angle. So, the law of reflection doesn’t hold true. Thus, diffuse reflection.

(C) Diffuse reflection of light takes place.

Surface of cardboard in not smooth. Law of reflection doesn’t hold.

(D) Regular reflection of light takes place. 

In mirror (any type of mirror can be plane or concave or concave) law of reflection hold. So regular reflection takes place.

(E) Diffuse reflection of light takes place.

The surface of paper is not smooth. Law of reflection doesn’t hold.

Additional information:-

If you are thinking the paper is smooth than just remember - it is impossible to write on a smooth surface. Smooth surface means no friction. So, on the surface of mirror, we can consider as friction = 0. If the paper has zero friction that implies we cannot write on the paper.

(F) Regular reflection of light takes place.

The surface of the marble floor is covered with water and on the water surface law of reflection hold true.

Additional information:-

When the light fall on the surface of the water some part gets reflected and some part get refracted.

Both laws of reflection and law of refraction hold true for water.

Laws of reflection are: 

→ The angle of reflection is always equal to the angle of incidence. 

→ The incident ray, the reflected ray and the normal to the reflective surface at the point of incidence all lie in the same plane.

While watching TV or computer a simple rule 20 – 20 – 20 helps us in protecting eyesight. After 20 minutes of watching TV or computer screen, take 20 seconds break and watch the TV or computer around 20 feet away.

Concave mirrors: 

1. Concave mirrors are used while applying make – up or shaving, as they provide a magnified image. 

2. They are used in torches, search lights and head lights as they direct the light to a long distance.

Convex mirrors: 

1. Convex mirrors are used in vehicles as rear view mirrors because they give an upright image and provide a wider field of view as they are curved outwards. 

2. They are found in the hallways of various buildings including hospitals, hotels, schools and stores. They are usually mounted on a wall or ceiling where hallways make sharp turns.

(a) Regular reflection 

A polished surface is an example of a smooth surface. A polished wooden table has a smooth surface. Hence, reflections from the polished table will be regular. 

(b) Diffused reflection 

Chalk power spread on a surface is an example of an irregular surface. It is not smooth. Therefore, diffused reflection will take place from chalk powder. 

(c) Diffused reflection 

Cardboard surface is also an example of an irregular surface. Hence, diffused reflection will take place from a cardboard surface. 

(d) Regular reflection 

Marble floor with water spread over it is an example of a regular surface. This is because water makes the marble surface smooth. Hence, regular reflection will take place from this surface. 

(e) Regular reflection 

Mirror has a smooth surface. Therefore, it will give a regular reflection. 

(f) Diffused reflection 

Although a piece of paper may look smooth, but it has many irregularities on its surface. Due to this reason, it will give a diffused reflection. 

Answer:

The diffused reflection is not due to the failure of laws of reflection but caused by irregularities in the reflecting surface

The correct option is B) cloth.

No the magnifying glass reflect the light falling on it.

(b) Concave mirror

No all the objects reflect the light rays falling on it.

1. Concave mirrors are used by ENT doctors as Head mirrors. 

2. They have this mirror strapped on their head. 

3. Light from the bulb is made to fall on the mirror gets reflect from it. 

4. This reflected light is focused into the throat or ear of the patient. So that the doctor can examine inner parts clearly.

The kaleidoscope gives a number of images formed by reflection from the mirrors inclined to one another. Designers and artists use kaleidoscope to get ideas for new patterns to design wallpapers, Jewellery and fabrics.

(a) Rough surface

1) Characteristics of image formed by a concave mirror : 

A concave mirror forms real and virtual images, erect and inverted images, smaller, same size and bigger images depending on the position of object infront of it. 

2) Characteristics of image formed by a convex mirror : 

A convex mirror always forms virtual, erect, smaller image irrespective of the position of the object.

The properties of images formed by concave mirror.

1. It can form both real and virtual images. 

2. It produces erect and inverted images 

3. It also produces small same size and bigger images depending on the position of object in front of it.

The correct option is A) Image distance.

(d) All of these

The correct option is C) concave mirror.

The correct option is B) convex mirror.

Use of concave mirror:

A concave mirror is used by dentists to examine the teeth.

Use of convex mirror:

A convex mirror is used as a side-view mirror in 

vehicles.

The correct option is B) convex mirror.

Regular reflection:

1. When a beam of light (collection of parallel rays) falls on a smooth surface, it gets reflected. after reflection, the reflected rays will be parallel to each other.

2. Here, the angle of incidence and the angle of reflection of each ray will be equal.

3. Hence, the law of reflection is obeyed in this case and thus a clear image is formed.

4. This reflection is called 'regular reflection' or 'specular reflection'.

Example : Reflection of light by a plane mirror and reflection of light from the surface of still water. 

Irregular reflection: 

1. In the case of a body having a rough or irregular surface, each region of the surface is inclined at different angles. 

2. When light falls on such a surface, the light rays are reflected at different angles. In this case, the angle of incidence and the angle of reflection of each ray are not equal.

3. Hence, the law of reflection is not obeyed in this case and thus the image is not clear. Such a reflection is called ‘irregular reflection’ or ‘diffused reflection’.

Example : Reflection of light from a wall.

(a) Regular relfection