AP 8th Class Physical Science Notes Chapter 7 Light
→ Angle of Incidence : The angle between the normal and incident ray is called the angle of incidence (∠i).
→ Angle of Reflection : The angle between the normal and the reflected ray is known as the angle of reflection (∠r).
→ Blind Spot : At the junction of the optic nerve and the retina, there are no sensory cells, so no vision is possible at that spot. This is called the blind spot.
→ Braille : Braille is an education system for Visually impaired persons.
→ Cones : The cells contained in the retina are sensitive to bright light and colour.
→ Cornea : The transparent front part of the eye is called the cornea.
→ Diffused or Irregular Reflection :
→ Incident Rays : The light ray, which strikes any surface, is called the incident ray.
→ Iris : The dark muscular structure behind the cornea is called the IRIS.
→ Kaleidoscope : A kaleidoscope is a device that can form multiple images by multiple reflections.
→ Lateral Inversion : The image formed by a mirror on the left of the object appears on the right and the right appears on the left. This is known as lateral inversion.
→ Laws of Reflection :
- The angle of incidence is always 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.
→ Pupil : The small opening in the iris is called the pupil.
→ Reflected Rays : The ray that comes back from the surface after reflection is known as the reflected ray.
→ Reflection : The phenomenon of bouncing a light ray on a surface is called the reflection of light.
→ Regular Reflection : A reflection from a smooth surface like that of a mirror is called regular reflection.
→ Retina : Retina is the back part of the eye that catches the images and sends them to the brain.
→ Rods : The cells contained in the retina which are sensitive to dim light.
→ It is only when light from an object enters our eyes that we see the object.
→ A polished or a shiny surface can act as a mirror.
→ A mirror changes the direction of light that lalls on it.in The light ray, which strikes any surface, is called the incident ray.
→ The ray that comes back from the surface after reflection is known as the reflected ray.
→ It The angle between the normal and incident ray is called the angle of incidence (4).
→ The angle between the normal and the reflected ray is known as the angle of reflection (∠r).
→ In Angle of incidence is always equal to the angle of reflection. This is one of the laws of reflection.
→ The incident ray, the normal at the point of incidence and the reflected ray lie in the same plane. This is another law of reflection.
→ The image formed by a mirror the left of the object appears on the right and the right appears on the left. This is known as lateral inversion.
→ When all the parallel rays reflected from a rough or irregular surface are not parallel, the reflection is known as diffused or irregular reflection.
→ Reflection from a smooth surface like that of a mirror is called regular reflection.
→ Images are formed by regular reflection.
→ The objects which shine in the light of other objects are called Mluminated objects. Eg: moon
→ The objects which emit their own light are known as luminous objects. Eg : sun
→ The periscope makes use of two plane mirrors.
→ So many numbers of images formed by mirrors placed at an angle to one another is used in a kaleldoscope to make numerous beautiful patterns.
→ Sunlight (white light) consists of several colours.
→ Eye is one of our most important sense organs.
→ The eye has a roughly spherical shape.
→ The transparent front part of the eye is called the cornea.
→ The iris controls the amount of light entering into the eye.
→ Behind the pupil of the eye is a lens which is thicker in the centre.
→ The lens focuses light on the back of the eye, on a layer called retina.
→ There are two kinds of cells in the retina –
- cones, which are sensitive to bright light and
- rods, which are sensitive to dim light.
→ Cones sense colour,
→ At the junction of the optic nerve and the retina, there are no sensory cells, so no vision is possible at that spot. This is called the blind spot.
→ The impression of an image does not vanish immediately from the retina. It persists there for about 1/6th of a second.
→ The most comfortable distance at which one can read with anormal eye is about 25 cm
→ With suitable corrective lenses, these defects of the eye can be corrected.
→ Lamp or a laser torch can injure the retina.
→ Lack of vitamin A in foodstuff is responsible for many eye troubles like night blindness.
→ Raw carrots, broccoll and green vegetables and cod liver oil are rich in vitamin A.
→ Eggs, milk, curd, cheese, butter and fruits such as papaya and mango, are also rich in vitamin A.
→ Optical aids include bifocal lenses, contact lenses, tinted lenses, magnifiers and telescopic aids.
→ The most popular resource for visually challenged persons is Braille.