JSS 2: Light energy (I)
Sources of light
There are various sources of light, namely:
1. Natural sources e.g. sun, stars, fire-flies, etc
2. Artificial sources e.g. candles, electric torches, electric lamps, fluorescent lights, etc
Transmission of light
Light travels at a speed of 3.0 x 10⁸m/s in a vacuum or space and through a material medium
Transparent objects: They are objects that allow light to pass through them and objects can be easily seen through them.
Examples: glass, water, air, lenses, etc
Translucent objects: They are objects that allow light to pass through them but objects cannot be seen through them
Examples: frosted glass, tissue paper, tinted car windows, etc
Opaque objects: They are objects that do not allow light to pass through them and objects can not be seen through them.
Examples: wood, leather, metal sheets, walls, etc
Rays and beams of light
A light ray is the direction or path along which light energy flows.
Beam of light
A beam is a collection of rays of light.
Types of beam
There are three types of beams, namely:
1. Parallel beam
2. Convergent beam
3. Divergent beam
Parallel beam
A parallel beam is one in which the light rays are parallel to one another
Convergent beam
A convergent beam is one in which the rays converge or meet at a point
Divergent beam
A divergent beam is one in which the light rays all come from a point and spread out or diverge from the source
Reflection of Light
Reflection of light is the sending back of light rays when it hits a surface.
Types of reflection of light
The two types of reflection of light;
1. Regular reflection
2. Irregular (diffuse) reflection
Regular reflection: Reflection is said to be regular when light rays hit a smooth or highly polished surface and bounce off from it, as a parallel beam in the same opposite direction.
Laws of reflection of light
1. The incident ray, the reflected ray, and the normal at the point of incidence all lie on the same plane
2. The angle of incidence is equal to the angle of reflection.
r= angle of reflection
Example: The incident angle of an incident ray is 60°, calculate:
(i) angle of reflection
(ii) angle between the incident ray and the reflected ray
(iii) angle between the incident ray and the plane.
Solution
(i) From the second law of reflection, i = r.
Therefore: the angle of reflection = 60°
(ii) angle between the incident ray and the reflected ray = i + r
= 60° + 60°
= 120°
(iii) angle between the incident ray and the plane = 90° - 60°
= 30°
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