Define light?
- Light is a form of energy.
- It enable us to see the objects around us.
- When light falls on any object , the object reflects the sunlight falling on it in all the directions.
- So light enables us to see the object from which it reflected.
Define Reflection?
Reflection is the phenomenon of bouncing back of light in the same medium in which it was travelling when it falls on the surface.
Important terms
Incident ray
The Ray of light that falls on the mirror reflecting surface is called Incident ray.
Point of incidence
The point at which the incident ray strikes the reflecting surface of the mirror is called point of incidence.
Reflected ray
The Ray of light which is sent back after reflection by the mirror is called reflected ray.
Normal:
Normal is a line drawn at right angle perpendicular to mirror surface at the point of incidence.
Angle of incidence:
The angle which the incident ray makes with the normal at the point of incidence is called angle of incidence.
Angle of reflection
The angle which the reflected ray makes with a normal at the point of incidence is called as angle of reflection.
State the Laws of reflection?
There are two laws of reflection
- The angle of incidence is equal to the angle of reflection
- The incident ray the normal at the point of incidence and the reflected ray all lie in the same plane
What are the characteristics of image formed by plane mirror?
1. The image on a plane mirror is of the same size and the shape as the object
2. The image on a plane mirror is erect
3. The image formed on the plane mirror is virtual that is the image formed cannot be obtained on the screen
4. The image formed on a plane mirror is at the same distance behind the mirror as the object is in front of it
5. The image on a plane mirror is laterally inverted with respect to the object
Define lateral inversion?
Image formed by mirror, left of object appears on right and right of object appears on the left. The left right reversal of an object and its mirror image is called lateral inversion.
Formation of images on the plane mirror:
1. When we look into plane mirror, we can see our image behind the mirror.
2. When you more towards the mirror, image also move towards the mirror.
3. When you move away from mirror the image also moves away from mirror.
4. The distance of your image from the mirror is equal to your distance from the mirror.
Difference between regular and irregular reflection?
Regular reflection | Irregular or Diffused reflection |
The phenomena due to which parallel beam of light striking a smooth and highly polished surface is reflected back as a parallel beam of light is called regular reflection of light. | The phenomena due to which parallel beam of light striking on a rough surface gets reflected in various directions is called irregular or diffused reflection. |
The reflecting surfaces smooth and highly polished like a mirror. | The reflecting surface is not smooth but irregular like a cardboard |
All parallel rays reflected from smooth surface or parallel. | All parallel rays reflected from rough or irregular surface are not parallel. |
Images are formed | Images are not formed. |
Difference between luminous and non luminous object?
Luminous object | Non luminous object |
Objects that limit light on their own are called luminous object. | Objects that do not give it light on their own or called non luminous object |
Example Sun, Star, Candle, Electric bulb Torch etc.. | Example Table, Chair, Pencil, Bag etc.. |
How Moon a Non luminous object emit light ?
Moon is there non luminous object and does not have light on its own. When sunlight falls on the moon, it reflects the sunlight and hence we able to see the moon.
What are multiple images?
1. When two mirrors are inclined to each other at an angle many images of the object are seen. The image formed in one mirror act as an object for the other mirror. Hence multiple images are formed.
2. By varying angle between two mirror we can get multiple number of images.
3. When an object is kept in between two mirrors placed perpendicular to each other three images are formed.
4. When pair of mirror is placed parallel to each other infinite number of images are formed due to multiple reflections.
5. Actual number of images formed depend upon angle between mirror.
Number of images (n) = 3600
———————– -1
Angle between mirror
List the applications of Multiple images?
1. Kaleidoscope is a device based on multiple reflections.
2. Mirrors inclined to each other at an angle 600
3. Mirrors form multiple images of object in front of them.
4. This creates beautiful pattern which change when the Kaleidoscope is rotated or shaken.
5. Designers of wallpaper, fabric, artist use Kaleidoscope to get ideas for new patterns.
List some uses of plane mirror?
1. Plane mirror are used as looking glass.
2. Plane mirrors are used as reflectors in solar cookers.
3. To provide false dimension when workplaces very small plane mirrors are used.
4. Plane mirrors are used for the construction of Periscope, Kaleidoscope etc.
5. Plane mirrors are used in barber shop to show the customer the back of his head.
6. Plane mirrors are used to provide false dimension in show cases displaying jewellery, wrist watch, spectacles etc..
Light reflection causes brightness and sparkle by keeping to mirrors facing each other when fixed on the opposite walls of the showcase.
Define Dispersion of light?
The phenomenon of splitting up of white light into its component colours on passing through transparent medium like glass prism is called dispersion of light.
Define the Spectrum of white light?
A band of seven colours formed on white screen when white light passes through the prism or any transparent medium is called Spectrum of white light.
Human Eye
- It is a light sensitive organ.
- It helps us to see the world around us.
- Eyelids act as shutter of eye and protect them from shock, injuries and bright light.
- Eyeball is spherical in shape and has diameter of 2.5cm.
- Outer part of eye has 3 layers. Sclera, Choroid and Retina.
1. list the structure and function of each part of eye?
1. Sclera:
- Outer most covering of eye. It is made up of white fibrous tissues.
- To protects the internal parts of eye from external injuries.
2. Choroid:
- Dark grey pigmented layer attached to sclera on its inner side is choroid.
- It is richly supplied with blood vessels and darkens the eye, protect the eye from internal infection.
3. Cornea :
- Sclera layer continues in front of eye as cornea. A transparent white bulge on the surface of eyeball.
- It allows the light to enter into the eyeball.
4. Retina:
- Innermost delicate membrane has rods and cones cells.
- Cones are sensitive to bright light
- Rods are sensitive to dim light.
5. Iris:
- Iris is present behind the cornea.
- It gives colour to eyes when pigmentation is highest, it gives black / brown color. when pigmentation is less, it gives blue colour to Iris.
6. Pupil:
- Iris has a central circular aperture called Pupil.
- Iris regulates the amount of light entering eye by adjusting size of pupil in 2 ways.
(i) Light is dim = Iris expands the pupil by allowing more light to enter the eye.
(ii) Light is bright = Iris contract the pupil and decrease the amount of light entering the eye.
7. Crystalline lens:
- A transparent double convex lens is situated behind the Iris.
- It help in position with help of ciliary muscles.
8. Suspensory ligaments:
Along with ciliary muscles, Suspensory ligaments are attached to lens.
9. Ciliary muscles:
- These muscles hold eye lens in proper place.
- Focal length of eyelens can be changed with help of cillary muscles according to distance of object in front of eye.
- When ciliary muscle contract, Eyelens becomes thick and the focal length decreases
- When ciliary muscle is relaxed, Eye lens becomes thin and the Focal length increases.
10. Optic nerve:
- It consists of one million nerve that connects to Rods and cones of retina to the brain
- Its function is to carry optical messages in form of electric signals to the brain.
11. Aqueous Humour
Space of eye between cornea and eyelens is filled with clear watery fluid called aqueous Humour.
12. Vitreous Humour
Space between Retina and lens is filled with fluid called vitreous fluid. It keeps eye wet and occupies 2/3rd of volume of eye
13. Blindspot:
At junction of optic nerve and retina, there are no sensory cells so no vision possible at that spot. It is Blindspot.
2. State the Working Of Human Eye ?
- Light from an object enter the eye through cornea and pupil.
- Lens focuses the light rays to form real Inverted and diminished image on retina.
- The Sensory cells (Rods & cones) of retina get activated and generate electric signals.
- Optic nerve send electric signal to brain.
- Brain interpret these signals and render erect image of object.
3. How do Owls see in dark?
- Owls retina has large number of rods, and few cones.
- Therefore, It can see in dim light but not in bright light.
- Owls have large cornea and large pupil that allows more light to enter the eyes and enable to see in darkness.
4. Define Persistence of vision?
- When light from object falls on retina, image impression does not vanish quickly from retina, impression clast for 1/16th of a second
- So when stationary images of moving object are flashed on eye at rate faster than 16 images per second, eye perceives this object as moving and it is called as Persistence of vision.
5. What is called as Power of Accommodation?
Ability of eye lens to adjust its focal length, so as to see objects located anywhere is called Power of accommodation.
6. Difference between Near point of eye and Far point of eye?
Near Point of Eye | Far Point of Eye |
Minimum distance at which eye can see objects very clearly without strain is called as Near point of eye. | Farthest point up to which an eye can see objects clearly without strain is called Far point of eye |
Near point is about 25cm. | Far Point is Infinity |
7. Difference between Near Sightedness and Far Sightedness ?
Near Sightedness | Far Sightedness |
It is also called as Myopia | It is also called as Hypermetropia |
Person can see nearby objects but cannot see distant objects. | Person can see distant objects clearly but cannot see nearby objects. |
In Myopia eye, image is formed in front of retina. | In Hypermetropic eye, image is formed behind the retina. |
To correct this Myopic condition, person can wear spectacles with concave lens. | To correct this Hypermetropic condition, person can wear spectacles with convex lens. |
8. What is Cataract?
- The eye lens becomes cloudy among age of 45 or above adults.
- It can even lead to blindness.
- Due to cloudiness in eye lens, light rays do not pass easily through lens to focus on retina.
- So people with cloudy eye lens are said to have Cataract
9.List few ways to take care of eyes?
- Always sit straight while reading/writing
- Do not lie down while reading, it can strain the eye
- Do not read in dim / very bright light.
- Do not watch TV / read for long time.
- Watch TV from 6 feet distance.
- Do not rub your eyes, it can lead to infection.
- Wash your eyes with clean water.
- When you feel strain while reading/writing use spectacles.
- Eat Foods that is rich in Vitamin A, Spinach, Red carrot, Broccoli, Cod liver oil, Egg, Milk, Cheese, Curd, Butter, Papaya, Mango etc.
11. What causes Night Blindness?
- Lack of Vitamin A is responsible for serious eye problems.
- Patient are unable to see properly at night or in dim light. This condition is called Night Blindness.
- It is followed by extreme dryness of eye, softening and clouding of cornea leading to complete blindness.
12. Who are Visually challenged people?
- Visually challenged people people who cannot see are called visually challenged people or blind people.
- Blindness is of two types curable and Non curable
13. How a blindness can be cured?
- When either cornea or eyelens become opaque due to some diseases it can be cured.
- If the crystalline lenses is opaque it can be removed surgically and replaced by artificial lens
- If cornea is opaque it is removed surgically and grafted from a healthy donar.
- Incurable blindness means complete or total loss of vision by birth or in later life due to diseases
14. Write a short note on Eye donation?
- Eyes can be donated by any person as a valuable gift to the visually challenged person
- Eye donars can belong to any age group social status and sex
- Person who were spectacles also can donate eyes
- People suffering from AIDS leukaemia tetanus cannot donate eyes.
- Donars eye are removed within 4 to 6hours after his or her death.
- Registered your eye for donation in eye bank and inform this to your friends or relatives so that your eyes can be donated.
15. What are the technological age available for visually challenged people??
Braille system:
- This system was invented by Louis Braille
- He lost his eyesight when he was a child.
- Braille is a system of representing characters by raised dots.
- Combination of raised dots in six dot cell makeup different characters.
- Books and periodicals or available in Barille.
🦯 White Cane:
- It is a long stick with Red tip to improve mobility.
- The visually challenged people used this to detect obstacles on the way while walking.
- With this cane, they can travel safely confidently and independently at home and other places.
Talking devices talking equipments such as talking thermometer talking watches clock calculator and compass are used by visually challenged people.
Computer
- Several softwares like Oralux and Adrian Knoppix are developed to access the information available on the Internet.
- Screen reading softwares are available to use mainstream computer applications including the internet.
Radio reading services
 There are over 100 radio reading services throughout the world they provide visually challenged people with readings from periodicals over the radio.
Important Links: