Optical Instruments and Phenomena: A Comprehensive Study
Periscope
Periscopes use isosceles rectangular glass prisms with a critical angle of approximately 43 degrees. The light inside the glass normally follows the path shown in the accompanying figure.
Pinhole Cameras
The simplest optical device is a pinhole camera, which is a closed box with a hole in one wall. It always produces real and inverted images, and its gain is given by A = y’ / s’.
Microscope
A microscope is used to see a greatly magnified image of a very small object at a short distance. It can be constructed of two converging lenses: the objective and the eyepiece.
The object is located at a distance slightly greater than the objective’s focal length. The image can coincide with the object focus of the eyepiece, in which case the eye forms an image at infinity, and the eye observes with no accommodation.
Terrestrial Telescope
The terrestrial telescope is an optical system that uses an inverter pair between the objective and the eyepiece. The inverter pair consists of two convergent lenses of the same power, separated by the sum of their focal lengths. It is sandwiched between the objective and the eyepiece, as shown in the figure.
The image formed by the objective lens coincides with the focus of the first lens of the inverter pair, and this is the object of the second lens. The image of the second lens is observed through the eyepiece, whose center coincides with the focus of the second lens of the inverter pair. With this system, the images are upright, and as shown in the figure, the eye acts without accommodation.
Myopia
Myopia results from a deformation caused by the elongation of the eyeball. The myopic eye focuses properly on the retina for near objects. However, the focal point for distant vision is formed in front of the retina. The consequence of this is blurred vision of distant objects. Divergent lenses are the solution.
Hyperopia
Hyperopia is the opposite of myopia. That is, the second focal point of the eye is behind the retina. As a result, the hyperopic eye sees well from afar but poorly up close. This defect can be overcome with converging lenses.
Magnifier
To increase the size of the observed image, one would have to increase the value of the angle. This could be achieved by bringing the object closer to the eye, but at the expense of losing the sharpness of the image. However, it can be done using a convex lens.
Young’s Experiment
Young’s experiment, also called the double-slit experiment, was conducted in 1801 by Thomas Young in an attempt to discern the wave or particle nature of light. Young found an interference pattern of light from a distant source diffracted by two slits, a result that contributed to the theory of the wave nature of light.
Young passed light from a single source through two narrow slits separated by a distance ‘a’. He obtained two coherent sources because the light came from a single real source. He was able to observe a pattern of alternating bright and dark stripes, or an interference pattern.
Diffraction of Light
Another crucial event that demonstrated the wave nature of light was diffraction. If the nature of light were purely corpuscular, particles passing through an opening in a straight line onto a screen would only show the light projection of the opening.
Reflection
In reflection, the angle of incidence (i) and the angle of reflection (i’) are equal.
Refraction
In refraction, when light passes from air to water, Newton argued that the corpuscles were attracted to the water and instantly accelerated upon crossing the boundary between the two.