Energy is the capacity to do work, Light is a form of energy because it can do work. Light energy travels on a straight line, the phenomenon of light travelling on a straight line is called rectilinear propagation of light. The pinhole camera operates on this principle. Other phenomena that show that the light travel in a straight line are the formation of shadows and eclipses. A ray of light is a straight line along which a light ray travels. A bean of a collection of parallel rays of light moving close together A bean a light may be
Table of Contents
(1) Parallel – When the rays of light travel parallel, Parallel bean
- Convergent of rays – when the rays of light meet at a point
3. Divergent rays – When the rays of light spread from a point away from each other
CONCEPT OF LIGHT TRANSMISSION
When light rays fall on a surface it may result to the following
(i) Reflection_ This is the sending back of rays of light from a smooth or highly polished surface on which it falls e . g mirror or other smooth surface
(ii) Refraction – This is the passage of light rays from one medium to another. It makes the light rays to appear bent . eg light rays from air to water. This is the reason why a stick or coin put in a glass of water appeared raised.
(iii)Transparent objects-These are objects that can allow light rays to pass through them .Those objects are said to be transparent, e g glass and clear water.
(iv)Opaque objects-These are objects that do not allow light to pass through them rather it absorbs the light rays, eg wood ,brick wall. cloth and cardboard
(v)Translucent objects-These are objects which allow light to pass through them but the object from which the light comes cannot be seen. Example oil paper ,wax paper, and glass sheets used for certain windows in the house
NATURAL LUMINOUS OBJECTS
Luminous objects are objects that produce light of their own .Example s are sun, stars and some living creatures such as glow-worm and fire-fly.
Artificial Luminous objects are objects such as electric lamps, kerosene lamp and candles
Non-luminous objects are are those objects that cannot produce light of their own e.g. moon.
REFLECTION OF LIGHT -When a ray of light strikes a surface is reflected back. The reflection may be regular or diffuse.
REGULAR reflection is when a parallel ray of light is reflected in the same direction when fall on smooth surface or highly polished surface.
| i |
| r |
| Normal |
| Reflected ray |
| incident ray |
DIFFUSE reflection occurs when a parallel ray of light is reflected in different directions , the rays become scatered or diffuse.
mirror
I= Angle of incidence is the angle incident ray make with the normal r= angle of refection is the angle between the normal and reflected ray . Both I and r are equal
Refraction of light Refraction is the change in the direction of light when it passes from one medium to another . Example be of medium that can refract a light ray is pond or swimming pool The law of refraction
- The incident ray and the refracted ray are all on the refracted rays are on the opposite side of the normal . The normal is the line drawn to be at right angle to the boundary or both materials
- The angle of incident is equal to angle of refraction
- The ratio of the sine of the angle of incident (i) to the sine of angle of refraction (r0) is referred to as refractive index refractive index “n” = sinio/sinro
APPARENT DEPTH
When a coin is put in a transparent cup or container containing water . When viewed from the top , the coin appears raised up, in which case its depth is loss than the actual depth of the coin at the bottom of the beaker . The depth at which it appeared to be seen by the eye is called Apparent depth
Dispersion and rainbow
When a ray of while light passes a glass prism especially triangular prism . The ray of light is splited into seven component color . The phenomenon is called dispersion of light . The series of color into which while light is splited is called a spectrum the component colors are red, orange, yellow, green, blue, indigo and violent ( VIGBYOR) The Same phenomenon cause formation or rainbow it happened when sin rays pass through water droplet in The atmosphere . The seven color of rainbow formed in the sky by droplet of water which hang in the
Atmosphere
VIOLET
INDIGO
GREEN
BLUE
ORANGE
RED
Colour prism are rectangular or triangle blocks of glass which change the direction of a light ray when it passes through them from another medium e. g air to glass . The prism bend light rays and produce colored image the image the rainbow color
Mechanism of Seeing
Light rays from an object enters the eye through the cornea which causes the light rays to be refracted and pass through the aqueous humour which further
Bends the light rays before entering the lens through the pupil. The lens further bends the light rays and focuses them on the retina especially on the yellow spot. The light rays passes through the vitreous humuor .Further bending of the light rays occurs again. The light rays on reaching the retina stimulates the rods and cones forms an inverted image on the retina .The inverted image is smaller in size than the object. Impulses are sent through the optic nerves the optic lobes of the brain, then to visual cent cerebral hemisphere where the actual size and colour of the image are interpreted correctly
ASSIGHNMENTS
1. Which of the following is the reason a clear pool of water is dangerous for amateur swimmers A.it is unsuitable for swimming B.it appear to be shallower than its real depth C.it always contain dangerous fishes D. it frightens young swimmers.
2. On which of the following does normal human eye forms its own image? A. lens B. pupil C. retina D. rainbow
3. When light passes through air to water or glass, there is A. reflection B. problem C. incidence D. refraction.
4. The separation of white light into various component of colours through a glass prism is known as A. dispersion Convergent Divergent Spectrum.
5 a. Explain why spoon in a glass cup of water appears to be bent
b. How does eye see objects both far and near
c. Explain the meaning of dispersion of light . How does it relate the rainbow in the sky?.
- Mention four properties of light
- State the laws of reflection
- What is refraction
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