Young's Double-Slit Experiment and Basic Optical Principles

Young's Double-Slit Experiment

The double-slit experiment of Young: The experiment consists of coherent light passing through two slits spaced a certain distance apart. When projected on a screen, the light that passes through the slits produces alternating bright and dark regions.

As the difference in distance traveled from each slit changes, the waves interfere. When the path difference leads to destructive interference, dark fringes appear; when the interference is constructive, bright fringes appear.

Elements of a Centered Optical System

The elements of a centered optical system are:

• Optical axis: The line on which the system has spherical symmetry. It passes through the optical center and the centers of curvature of the surfaces.
• Optical center: The intersection of the mirror, diopters, or thin lens with the optical axis.
• Center of curvature: The center of the spherical surface to which a mirror or lens surface (diopter) belongs. There can be centers of curvature on both sides of an element.
• Radius of curvature: The radius of the spherical surface to which the mirror, diopter, or thin-lens face belongs.

For the object and image positions we use the letters s and s'. For the sizes of object and image we use y and y'. By sign convention, positions measured to the left of the optical center are negative and to the right are positive. For sizes, the upper half is positive and the lower half is negative.

Operation of the Human Eye

Operation of the human eye: The human eye provides correct vision when it focuses the image on the retina. Objects we wish to see can be at different distances; the lens of the eye (the crystalline lens), by the property called accommodation, can alter its thickness and shape, thereby changing its focal length to focus rays on the retina.

The pupil opens or closes depending on the brightness. This variation of focal length is an involuntary process performed by the ciliary muscles. The limits of accommodation are the near point and the far point. Any object between these two points may be focused on the retina.

The near point is the point closest to the eye that can be seen with sharpness; it varies from person to person and generally moves farther away with age. For a normal eye, the far point is at infinity.

Myopia (Short-Sightedness)

Myopia: Distance vision appears blurred because the image is formed anterior to the retina. Correction is achieved by fitting a diverging (concave) lens of appropriate power.

Hyperopia (Long-Sightedness)

Hyperopia: Near vision is poor because the image forms behind the retina. Correction is done with a converging (convex) lens of appropriate power.