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Introduction:
Scientists and engineers have been able to enhance our lifestyles by understanding and using the Laws, Concepts and Principles of Optics and how they are applied in Optical Instruments. The key concepts are:
a. Lights as a form of electromagnetic radiation
Electromagnetic radiation is a term used to describe a pair of electric and magnetic fields that promulgate together at the speed of light. This means that light holds electric and magnetic components. The accelerated movement of electric charges emits radiation. This radiation is visible to us as light.

Figure 1: electromagnetic waves
Time-varying electric fields can bring magnetic fields and vice-versa. Since both fields generate each other, they occur jointly and therefore, propagate as electromagnetic waves.
The electromagnetic radiation of light is a small part of the electromagnetic spectrum.
Like all wave phenomena, radiation is considered by its wavelength and its frequency f. Electromagnetic radiation promulgates at the speed of light c. The equation is: .
Application such as the sun emits most of its radiation in the visible range which our eyes recognize as the color of rainbow.
b. Law of reflection
The law of reflection states that when a ray of light strikes a plane mirror, the light ray is reflected off the mirror as such that the angle of reflection is equal to incidence angle. The diagram below illustrates the law.

Figure 2: angle of reflection=angle of incidence
In the diagram, the light approaching the mirror is the incident ray and the light leaving the mirror is the reflected ray. The line perpendicular to the mirror is the normal line. The angle between the incident ray and the normal line is the angle of incident and the angle of r...

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Rainbow color components are evident through dispersion of visible light and total internal reflection in prisms.
6. Refraction in lenses
The refractive index of lens is larger than air therefore refraction in lenses occurs differently. It happens when light moves parallel to the normal and is refracted through the focal point. If a ray passes through the optical center of the lens, the ray would continue without being refracted. The optical direction is the point on the normal where the incident direction of a ray is parallel to the emergent direction.

Figure 13: converging lens
In a convex lens, the rays are parallel to the axis (normal) and cross each other at a single point on the focal point. This is called converging lens.

Figure 14: diverging lens
In a concave lens, the light rays bend away from the normal. This is known as diverging lens.