INDIAN LANGUAGE SCHOOL
PHYSICS
GRADE: 8
CHAPTER -16 LIGHT NOTES
1. State the characteristics of the image formed by a plane mirror.
i.
Image is virtual and erect.
ii.
Image size is same as that of the object.
iii.
Image distance and object distance are the same.
iv.
It is laterally inverted.
2. State the laws of reflection.
The two laws of reflection are:
i.
ii.
The angle of incidence is equal to the angle of reflection.
Incident ray, reflected ray, and the normal drawn at the point of incidence to the reflecting
surface, lie in the same plane.
3. What is the principle used in kaleidoscope?
The formation of a number of images (multiple reflections) by mirrors placed at an angle(60⁰) to
one another is used in kaleidoscope to make beautiful patterns.
4. Name the different parts of the eye and their functions.
i.
Cornea: Light enters the eye through the cornea.
ii.
Iris: The function of the iris is to regulate the amount of light entering the eye.
iii.
Pupil: The size of the pupil is controlled by the iris.
iv.
Eye lens(convex lens): Its function is to focus the image of different objects
clearly on the retina.
v.
Ciliary muscles: The eye is held in position by the ciliary muscles. It helps in
changing the focal length of the eye lens to see far and near objects.
vi.
Retina: The function of the retina is to receive the optical image of the object
and then convert it to optical pulses.
vii.
Optic nerve: Optic nerve is the nerve that connects the eye to the brain and
carries impulse , to and fro the brain.
viii.
Yellow spot: Its function is to form a very clear image by sending a large number
of optical pulses to the brain as it has a good amount of nerve endings.
ix.
Rods and cones: Cone and rods are sensitized by bright light and generate
impulses that can be read by the brain. Cones sense colour and rods are
sensitive to dim light.
5. What is blind spot?
Blind spot is a region at the junction of the optic nerve and the retina, where there are no sensory cells,
so no vision is possible at this spot. This is called blind spot.
6. What is persistence of vision?
The impression of the image made on the retina does not vanish immediately. It persists on the retina
for approximately about 1/16th of a second. This property of the eye is called persistence of vision.
7. Define the following:
i. Angle of incidence: The angle between the incident ray and the normal at the point of incidence is
called the angle of incidence.
ii. Angle of reflection: The angle between the reflected ray and the normal at the point of incidence is
called angle of reflection.
iii. Reflection : The bouncing back of light into the same medium after striking a surface is called
reflection.
iv. Lateral inversion: The phenomenon of left appearing right and right appearing as left on reflection
from a plane mirror is called lateral inversion.
v. Dispersion of light: The splitting up of white light into its constituent colours is called dispersion.
vi. Regular reflection: When a parallel beam of light, on striking some smooth and polished surface, is
reflected as a parallel beam of light, such a reflection is called regular reflection. eg. Reflection taking
place on mirror, still water, highly polished surfaces.(diagram)
vii. Diffused or Irregular reflection: When a parallel beam of light on striking some rough surface, is
reflected in different directions, such a reflection is called diffused or irregular reflection. Eg. Reflection
from wall, stones, trees.(diagram)
viii. Dispersion of light : The splitting of white light into seven colours is called dispersion of light.eg.
rainbow.
8. Write the differences between real and virtual images.
Real Image
1. Formed when reflected or refracted rays
actually meet at a point.
2. Can be obtained on a screen.
3. It is always inverted.
Virtual Image
1. Formed when reflected/refracted rays
appear to meet from a point.
2. Cannot be obtained on a screen.
3. It is always erect.
9. Differences between regular and irregular reflection
Regular reflection
1. Give rise to clear image formation.
2. Formed on smooth and polished surface.
3. The reflected rays are parallel to each other.
4.diagram
Irregular reflection
1. Does not give rise to clear image formation.
2. Formed on rough and unpolished surfaces.
3. Reflected rays are scattered in different
directions.
4. diagram
10. What are the two defects of eye? How can it be corrected?
The two defects of the eye are short-sightedness (myopia) and long- sightedness (hypermetropia).
Correction: Myopia- using concave lens and hypermetropia using convex lens.
11. What is the difference between the eyes of the night birds and the day birds?
The day birds can see clearly during the day but not at night. The day birds have more cones and fewer
rods. The cones are sensitive to bright light and can sense colours. Night birds can see clearly at night
but not during the day. Their eyes have a large cornea and pupil to allow more light to pass. Also their
retina has mostly rods and few cones. Rods are more sensitive to dim light.
12. What is cataract of the eye? How can it be corrected?
Cataract is a condition in which the eye lens becomes cloudy. Light does not pass through the lens to
reach the retina. It can be corrected by replacing the lens with an artificial lens.