Light mind map by Ratna
Light-Tejas
There are two types of spherical mirrors
i) Concave mirrors
ii) Convex mirrors
Concave mirrors
There are two types of spherical mirrors
i) Concave mirrors
ii) Convex mirrors
Concave mirrors
A concave mirror is a spherical mirror whose reflecting surface is curved inwards. In a concave mirror, reflection of light takes place from the inner surface. This mirror resembles the shape of a ‘cave’. A Painted surface is a non-reflecting surface.
Convex mirrors
Convex mirrors
A convex mirror is a spherical mirror whose reflecting surface is curved outwards. In a convex mirror, the reflection of light takes place from its outer surface. A Painted surface is a non-reflecting surface.
The Definitions Of Terminologies
Pole of a spherical mirror
The central point of the reflecting surface of a spherical mirror is termed as the pole. It lies on the mirror and is denoted by the letter (P)
The Definitions Of Terminologies
Pole of a spherical mirror
The central point of the reflecting surface of a spherical mirror is termed as the pole. It lies on the mirror and is denoted by the letter (P)
Centre of curvature
The centre of curvature as the centre of a sphere from which the given spherical mirror (convex or concave) is obtained. It is denoted by the letter (C).
The centre of curvature as the centre of a sphere from which the given spherical mirror (convex or concave) is obtained. It is denoted by the letter (C).
Radius of curvature
The distance between the centre of curvature and pole (PC) is known as the radius of curvature.
Principal axis of the spherical mirror
The straight line joining the pole (P) and the centre of curvature (C) is termed as the principal axis.
The distance between the centre of curvature and pole (PC) is known as the radius of curvature.
Principal axis of the spherical mirror
The straight line joining the pole (P) and the centre of curvature (C) is termed as the principal axis.
Focus
The focus (F) is the point on the principal axis of a spherical mirror where all the incident rays parallel to the principal axis meet or appears to diverge from after reflection.
Reflection by spherical mirrors
The different ways in which a ray of light is reflected from a spherical mirror are:
Case I: When the incident light ray is parallel to the principal axis.
In this case, the reflected ray will pass through the focus of a concave mirror.
Case II: When the incident light ray passes through the focus of a concave mirror.
In this case, the reflected light will be parallel to the principal axis of the spherical mirror.
Case III: When the incident ray passes through or appears to pass through the centre of curvature.
Case IV: When the incident ray is normal to the reflecting surface.
The focus (F) is the point on the principal axis of a spherical mirror where all the incident rays parallel to the principal axis meet or appears to diverge from after reflection.
Reflection by spherical mirrors
The different ways in which a ray of light is reflected from a spherical mirror are:
Case I: When the incident light ray is parallel to the principal axis.
In this case, the reflected ray will pass through the focus of a concave mirror.
Case II: When the incident light ray passes through the focus of a concave mirror.
In this case, the reflected light will be parallel to the principal axis of the spherical mirror.
Case III: When the incident ray passes through or appears to pass through the centre of curvature.
Case IV: When the incident ray is normal to the reflecting surface.
Do you know?Radio telescope is a reflecting telescope that tends to reflect all parallel rays coming from distant stars, galaxies, deep space etc. to a single point. This is because the reflecting surface acts as a large concave mirror. The point where the reflected rays meet is its focus. A receiver is placed at the focus, which receives light rays and sends these rays to a computer in the form of electrical signals. As a result, images of a light source can be obtained on the monitor.
PPT by Ratna Raj
Image formation in concave mirror (PPT) by Ratna Raj
Images formed by Concave Mirrors -Tejas
source
A concave mirror can produce both real and virtual images.
I. When the object is at infinity
The light rays coming from infinity are parallel. When parallel light rays are incident on the reflecting surface of a concave mirror, they tend to meet at its focus after reflection. In this case, the image is formed at the focus, and is point-sized.
source
A concave mirror can produce both real and virtual images.
I. When the object is at infinity
The light rays coming from infinity are parallel. When parallel light rays are incident on the reflecting surface of a concave mirror, they tend to meet at its focus after reflection. In this case, the image is formed at the focus, and is point-sized.
II. When the object is behind the centre of curvature
The image is formed between the focus (F) and the centre of curvature (C). This image is real, inverted and diminished.
The image is formed between the focus (F) and the centre of curvature (C). This image is real, inverted and diminished.
III. When the object is at the centre of curvature
In this case, the image is formed at the centre of curvature. This image is real, inverted and of the same size as the object.
In this case, the image is formed at the centre of curvature. This image is real, inverted and of the same size as the object.
IV. When the object is between the centre of curvature (C) and the focus (F)
The image is formed behind the centre of curvature. This image is real, inverted and magnified.
The image is formed behind the centre of curvature. This image is real, inverted and magnified.
V. When the object is at the focus (F)
In this case, the image is formed at infinity. This image is real, inverted and highly enlarged.
In this case, the image is formed at infinity. This image is real, inverted and highly enlarged.
VI. When the object is placed between the focus (F) and the pole (P)
The image is formed behind the mirror. This image is virtual, erect and magnified.
The image is formed behind the mirror. This image is virtual, erect and magnified.
Images Formed by Convex Mirrors
A convex mirror always produces virtual and erect images of very small size.
I. When the object is at infinity
In this case, the image appears to form at the focus. This image is virtual, erect and very small in size
A convex mirror always produces virtual and erect images of very small size.
I. When the object is at infinity
In this case, the image appears to form at the focus. This image is virtual, erect and very small in size
II. When the object is between the pole (P) and a point X (X lies beyond C)
In this case, the image is formed between the pole (P) and the focus (F), behind the mirror. This image is virtual, erect and small in size.
In this case, the image is formed between the pole (P) and the focus (F), behind the mirror. This image is virtual, erect and small in size.
watch the glass slab experiment whenever you want........
by Ratna SOURCE: enliveeducation
Images formed by Convex Mirrors -Tejas
A convex mirror always produces virtual and erect images of very small size. The images formed by a convex mirror are primarily classified in two ways.
A convex mirror always produces virtual and erect images of very small size. The images formed by a convex mirror are primarily classified in two ways.
I. When the object is at infinity
In this case, the image appears to form at the focus. This image is virtual, erect and very small in size.
II. When the object is between the pole (P) and a point X (X lies beyond C)
In this case, the image is formed between the pole (P) and the focus (F), behind the mirror. This image is virtual, erect and small in size.
Mirror formula
In this case, the image appears to form at the focus. This image is virtual, erect and very small in size.
II. When the object is between the pole (P) and a point X (X lies beyond C)
In this case, the image is formed between the pole (P) and the focus (F), behind the mirror. This image is virtual, erect and small in size.
Mirror formula
- The distance of an object from the pole of a mirror is termed as the object distance denoted by ‘u’.
- The distance of an image from the pole of a mirror is termed as the image distance denoted by ‘v’.
Magnification
The magnification of a spherical mirror gives the relative extent to which the image of an object is magnified with respect to the object size.
m=image height/object height
Laws of refraction
There are two laws of refraction.
First law of refraction
The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant. This is known as Snell’s law. Mathematically, it can be given as follows:
Here, is the relative refractive index of medium b with respect to medium a.
Functions of some parts of the eye by RATNA RAJ
Differences between a camera and an eye by RATNA RAJ
Similarities between a camera and an eye by RATNA RAJ
EYE By RATNA RAJ
Lens by RATNA RAJ
Laws of Refraction by RATNA RAJ
RATNA RAJ: All the members and visitors please answer these questions...............
1. A ray of light passing through centre of curvature ......................... back.
2. The mirror used in the construction of astronomical telescopes is................. .
3. What is a focal plane?
4. What type of image is always formed by a convex mirror?
5. Name any 6 parts of an eye and write the function of ciliary muscles.
Answers of these questions will be soon available............................
2. The mirror used in the construction of astronomical telescopes is................. .
3. What is a focal plane?
4. What type of image is always formed by a convex mirror?
5. Name any 6 parts of an eye and write the function of ciliary muscles.
Answers of these questions will be soon available............................
Please write your answers in this text box
Do not forget to write your name before answering the questions
Do not forget to write your name before answering the questions
structure of human eye -Tejas
The Shape of the eye is roughly spherical with an average diameter of around 2.3 cm. The outer part of the eye is quite tough and white in colour. This white part of the eye is known as sclera. The transparent, front outer covering of the eye is known as the cornea. Behind the cornea, there is a colored membrane known as the iris. It regulates the amount of light entering the eye. It also gives colour to the eye. In the iris, there is a variable sized, black circular opening known as the pupil. Its size is controlled by the iris. It appears to be black in colour because most of the light entering it is absorbed by the tissues, which are present in the pupil.
The size of the pupil depends on the brightness of light. It opens and closes in order to regulate and control the amount of light entering the eye. When we enter a dimly lit room, it takes the iris some time to expand the pupil to allow more light to enter the eye. For this reason, it takes us a few seconds to clearly see objects in a dimly lit room.
The Shape of the eye is roughly spherical with an average diameter of around 2.3 cm. The outer part of the eye is quite tough and white in colour. This white part of the eye is known as sclera. The transparent, front outer covering of the eye is known as the cornea. Behind the cornea, there is a colored membrane known as the iris. It regulates the amount of light entering the eye. It also gives colour to the eye. In the iris, there is a variable sized, black circular opening known as the pupil. Its size is controlled by the iris. It appears to be black in colour because most of the light entering it is absorbed by the tissues, which are present in the pupil.
The size of the pupil depends on the brightness of light. It opens and closes in order to regulate and control the amount of light entering the eye. When we enter a dimly lit room, it takes the iris some time to expand the pupil to allow more light to enter the eye. For this reason, it takes us a few seconds to clearly see objects in a dimly lit room.
Behind the pupil there is a lens which is thicker at the centre. It is made up of living cells. TwoCiliary muscleshold the lens within the eye-ball. The eye lens being convex in nature converges the light rays’ incident on it. Hence, it focuses the light falling on it on a thin layer of nerve cells called the retina. The retina is made up of a large number of nerve cells. Light falling on these nerve cells stimulate two kinds of sensitive cells known as cones and rods. Rods are sensitive to low light levels. Cones are sensitive to bright light, but they sense colours. Sensation felt by them is transmitted to the brain in the form of electrical signals through the optic nerve. This allows us to see.
The point where the retina and the optical nerve meet each other is devoid of any sensory cells. Hence, vision is not possible from this point. This point is known as the blind spot.
Do You Know:
Animals use their eyes in a special way. Crabs have very small eyes, which are located on the head. This helps a crab to look behind. Butterflies have a large number of eyes. An Owl’s eye is composed of a large numbers of rod cells and a very few number of cones on the retina. Hence, it is not able to see in daylight.
The point where the retina and the optical nerve meet each other is devoid of any sensory cells. Hence, vision is not possible from this point. This point is known as the blind spot.
Do You Know:
Animals use their eyes in a special way. Crabs have very small eyes, which are located on the head. This helps a crab to look behind. Butterflies have a large number of eyes. An Owl’s eye is composed of a large numbers of rod cells and a very few number of cones on the retina. Hence, it is not able to see in daylight.
Why Do We Have Two Eyes ?
By RATNA RAJ
We need two eyes because a human being has a horizontal field of view of about 150 degrees with one eye and 180 degrees with two eyes. Thus, 2 eyes provide us wider horizontal view.
Defects of eye -Tejas
Myopia (short sightedness)
Myopia is a defect of vision in which a person clearly sees all the nearby objects, but is unable to see the distant objects comfortably and his eye is known as a myopic eye. A myopic eye has its far point nearer than infinity. It forms the image of a distant object in front of its retina as shown in the figure.
Myopia is caused by
- increase in curvature of the lens
- increase in length of the eyeball
a concave lens has an ability to diverge incoming rays, it is used to correct this defect of vision. The image is allowed to form at the retina by using a concave lens of suitable power as shown in the given figure.
Hypermetropia (Long sightedness)
Hypermetropia is a defect of vision in which a person can see distant objects clearly and distinctively, but is not able to see nearby objects comfortably and clearly.
Hypermetropia is a defect of vision in which a person can see distant objects clearly and distinctively, but is not able to see nearby objects comfortably and clearly.
Hypermetropia is caused due to
- reduction in the curvature of the lens
- decrease in the length of the eyeball
a convex lens has the ability to converge incoming rays, it can be used to correct this defect of vision, as you already have seen in the animation. The ray diagram for the corrective measure for a hypermetropic eye is shown in the given figure.
Presbyopia (Ageing vision defect)
Presbyopia is a common defect of vision, which generally occurs at old age. A person suffering from this type of defect of vision cannot see nearby objects clearly and distinctively. A presbyopic eye has its near point greater than 25 cm and it gradually increases as the eye becomes older.
Presbyopia is caused by the
Presbyopia is a common defect of vision, which generally occurs at old age. A person suffering from this type of defect of vision cannot see nearby objects clearly and distinctively. A presbyopic eye has its near point greater than 25 cm and it gradually increases as the eye becomes older.
Presbyopia is caused by the
- weakening of the ciliary muscles
- reduction in the flexibility of the eye lens
Cataract
It is also one of the eye defects found commonly in people of older ages. In this defect, the crystalline lens becomes milky and cloudy. This condition is also known as cataract. This causes partial or complete loss of vision. This loss of vision can be restored by removing the cataract by means of a cataract surgery. The use of any kind of spectacle lenses does not provide any help against this defect of vision.
It is also one of the eye defects found commonly in people of older ages. In this defect, the crystalline lens becomes milky and cloudy. This condition is also known as cataract. This causes partial or complete loss of vision. This loss of vision can be restored by removing the cataract by means of a cataract surgery. The use of any kind of spectacle lenses does not provide any help against this defect of vision.
Do you know why white light gets dispersed into seven colours?
When a beam of white light AB enters a prism, it gets refracted at point B and splits into its seven constituent colours, viz. violet, indigo, blue, green, yellow, orange, and red. The acronym for the seven constituent colours of white light is VIBGYOR. This splitting of the light rays occurs because of the different angles of bending for each colour.
When a beam of white light AB enters a prism, it gets refracted at point B and splits into its seven constituent colours, viz. violet, indigo, blue, green, yellow, orange, and red. The acronym for the seven constituent colours of white light is VIBGYOR. This splitting of the light rays occurs because of the different angles of bending for each colour.
- Twinkling of stars
Tyndall effectThe Tyndall effect is caused by the scattering of light by very small air particles, which are suspended in the Earth’s atmosphere. To observe the Tyndall effect, the particles diameter should be less than 1/20th of the wavelength of the light used.