Ray Optics and Optical Instrument

Ray Optics and Optical Instruments use a graphic of a ray of light to explain numerous phenomena such as reflection, refraction, and dispersion. Ray optics, also known as geometrical optics, argues that light travels in a straight path and each object has an image.

Let’s start with the behaviour of light. 

Characteristics of Light

• Light Always Travels in a Rectilinear Propagation

Light, on the whole, prefers to travel in a straight line. Light rays cannot continue their propagation if the path has curves or bends. This suggests that light prefers to propagate at a limited distance.

• No Need for the Medium

In any medium, light may travel. Even in a vacuum, light will move.

• Speed

There is no other energy source that can travel as quickly as light. Speed of light is expressed by ‘c’ and it is equal to 3 x 108 m/s.

Reflection of Light

A spherical mirror is divided into two curves when cut horizontally or vertically. Curved surfaces are those that feature a reflecting surface on one side and an objective surface on the other.

• Spherical Mirrors

A sphere includes a spherical mirror. When one of the surfaces is silvered, the other becomes the reflective surface. The mirror is called a concave mirror when the convex face is silvered and the reflecting surface is concave. The mirror is called a convex mirror when its concave face is silvered, and the convex face is the reflecting face.

• Centre of curvature.
• Normal.
• The radius of curvature.
• Pole of the mirror.
• Principal axis.

Refraction of Light

Refraction occurs when light is transferred obliquely from one medium to another, causing a perceptible shift in the image’s light path.

Laws of Refraction:

• The incident ray, the normal line, and the refracted image rage are all on the same plane.
• For a given medium, the ratio of sine angle of incidence to sine angle of refraction remains constant.

The ratio of the speed of light in a vacuum to the speed of light in the medium is known as the refractive index.

Snell’s law of refraction states that,

• For the refracting medium to incident medium, a refractive index is the ratio of sine angle of incidence to sine angle of refraction. r= n2/n1
• The absolute refractive index, on the other hand, refers to the ratio of the speed of light in a medium to the speed of light in vacuum. n = c/v

An absolute refractive index can be used to identify whether a medium is optically denser or rarer. If medium 1 has a greater absolute refractive index than media 2, that medium 1 is said to be optically denser. Medium 1 is said to be an optically rarer medium if its refractive index is lower than that of medium 2.

Examples:

Diamonds, prisms, optical fibre, mirage, etc.

Through spherical surfaces, refraction occurs.

Lens maker’s formula for the thin lens will be 1/f = [(n2-n1)/n1] (1/R1 – 1/R2)

Here n1 and n2 are the refractive index of two spherical mirrors. R1 and R2 are the curvature radius of the spherical mirrors.

For convex lenses, R1 is positive and R2 is negative, whereas for concave lenses, R1 is negative and R2 is positive.

The usage of a combination of lenses is beneficial in a variety of situations.

• Increasing the image’s magnification
• Increasing the sharpness of an image by reducing the flaws generated by a single image.
• Giving the constructed image about the thing
• Expanding the field of view.

Optical Instruments

In our daily lives, we employ a variety of optical devices that were created by combining the properties of reflection, refraction, and dispersion. The following are some of the devices:

• Eye

The intensity of light and colour is sensed by an array of interconnecting nerve fibres and cells in our eyes. The retina, for example, comprises rods and cones that take light, convert it to electrical signals, and transmit them to the brain via the optic nerves. In addition, the ciliary muscles aid in the modification of the shape and focal length of the lens in the eye.

• Lens

Lenses are made by two spherical mirrors.  Some of the most important phrases linked to lenses have been simplified to help you with your review. These are some of the terms:

• Centre of curvature.
• The radius of Curvature.
• Principal Axis.
• Optical centre.
• Principal foci.
• First principal focus F1.
• Second principal F2.
• Focal Length.

• Simple Microscope

A converging lens with a short focal length is used in a basic microscope, commonly known as a magnifying glass. As a result, when it is amplified and held close to the eye, an erect and virtual image is generated. A compound microscope, on the other hand, has two converging lenses, a moderate focal length and big aperture eyepiece, and a tiny focal length and short aperture objective lens.

• Telescope

This equipment is used to observe objects that are located at a great distance. A telescope, on the other hand, has an objective lens with a large aperture and a long focal length, as well as an eye lens with a tiny aperture and focal length.

Conclusion 

In this article we describe the light and its properties. In ray optics we study reflection and refraction of light through a spherical surface. Lens is constructed by two spherical surfaces. Lens are used in eye-glasses, microscopes and telescopes. 

Here you’ve learned about ray optics and optical instruments, behaviours of light, reflection, refraction, and more.