JSS3 Basic Science Lesson Note on Light Energy

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TOPIC:   LIGHT ENERGY

CONTENT:

1. Review of the concepts of (I) reflection (ii) refraction of light
2. The apparent depth and its dangers to swimmers.
3. Vision
4. Dispersion and rainbow.

 

Light is a form of energy. It enables us to see things when it is reflected from objects into

our eyes. Objects that give light by themselves are called luminous objects. E.g sun, while those that cannot give light but only reflect light from luminous objects are called non-luminous objects. E.g moon.

Reflection of light

Reflection is the sending back of rays of light after striking a reflecting surface. Reflection from a surface depends on how smooth or rough the surface is. A reflection from a smooth surface like a mirror is regular while that from rough surfaces like walls and stones is irregular or diffuse.

Light Rays

Light ray is the pathway through which light travels.  Light ray could be incident (ray from the light source) and reflected ray (ray from the reflected object). When rays are many they form beam. A beam is the collection of more than one ray. A beam could be convergent (rays meeting at a point), divergent (rays going out from a point) and parallel (rays moving in a straight line).  A substance that allows light to pass through it so that the object is seen clearly is called transparent object. Objects that does not allow light pass through it is called opaque object and those objects that allow light pass through it but the objects are not seen clearly is known as translucent objects.

There are two basic laws of reflection. These are:

1. The incident ray, the normal ray and the reflected ray at the point of incidence, all lie on the same plane.
2. The angle of incidence is equal to the angle of reflection

APPLICATIONS OF REFLECTION IN SOME OPTICAL INSTRUMENTS

For example:

1. The plane mirror is used as a dressing mirror because it shows a reflection of our image.
2. The simple periscope contains two plane mirrors facing each other, and inclined at an angle of 45⁰ to the horizontal. It is used to view beyond obstacles e.g. in submarines, simple periscopes are used to view ships on the ocean.
3. The sextant: this is used for finding the angle of elevation of the sun; it also consists of two mirrors.
4. The kaleidoscope: This is used for producing different colour patterns when turned. It makes use of plane mirrors inclined at 60⁰ to each other.

 Refraction of light

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