#### Applications of Light Waves, Physics tutorial

The Camera - Features and Operations:

The features and operations of the lens camera are as follows:

1) Comprise of a light - tight box that includes a convex lens in front and a film at the opposite end.

2) The lens converges the incident rays from the objects.

3) The film serves up as a screen on which the image is received.

4) Features of the image formed: Real, Inverted and Diminished.

5) Focusing screw modifies the distance of lens from film in order to for all time focus the image on the film.

6) Diaphram regulates the amount of light entering the camera. This is made possible through the variable aperture or hole.

7) Shutter regulates the amount of light entering the camera. It consists of variable speed and thus can open for various lengths of time (that is, exposure time).

The extent to which the diaphragm and the shutter join to find out the amount of light entering the camera based on:

• Sensitivity of the film
• Brightness of the object
• Type of effect that is wanted

The Projector - Features and Operations:

The projector is a tool for projecting on a screen an enlarged image of transparent object like a slide. That is a projector is utilized for representing enlarged image of transparent slides and films on a white screen.

1) A powerful source of light is necessary as light on the screen has to spread over numerous times greater than that on the slide (film) in order to accomplish the high magnification needed. The camera projector magnification could be as high as 100 times. The powerful however small light source illuminates the object that is generally non-luminous. A converging mirror placed behind the light source assists to direct the light to the film or slide. This source of light is at the focus of the first lens help the second lens converges the parallel beam on the projection lens. The convergent beam illuminates the slide (or film).

2) The projection lens is adjusted so that the slide (or film) is just beyond the principal focus.

3) The slide (or film) should be placed upside down in such a way that the image on the screen appears the right way up.

4) It is a tool to absorb the intense heat from the source of light is generally interposed between the condenser and the slide (or film) or a fan is incorporated to send a cooling draught on the slide (or film) to prevent it from over-heating.

5) Features of image formed: Real and Enlarged

The principle of the slide project is employed in cine-projector, photographic enlargers and some other devises.

Features and operations of the human eye:

1) The cornea is transparent and lets light rays to pass via to meet up the eye lens.

2) The eye lens focuses the image of the object on the retina.

3) The susceptible retina sends message to the brain by means of optic nerve.

4) The pupil is a hole in the middle of the iris. It seems black as no light is reflected from it.

5) The iris is the colored part of the eye. This adjusts the size of the pupil to differ the amount of light which enter the eye via the pupil.

6) The ciliary muscle modifies the focal length of the eye lens in order to focus images on the retina (that is, an action termed to as power of accommodation of the eye). The contraction and relaxation of the ciliary muscles differs the thickness of the lens (that is, the focal length).

7) The aqueous humor is a transparent liquid and fills the space between the cornea and the lens

8) The vitreous humor is a jelly-like substance which fills the space between the lens and the retina.

The action of the eye:

The normal eye in the relaxed state is mainly focused on infinity termed as the far point.

1) Near point and far point: The nearest point at which an object can be evidently seen is termed as the near point. The farthest point at which an object can be clearly seen is termed as the far point.

• To see near objects clearly, the ciliary muscles raise the curvature of the eye lens and therefore let it to focus the divergent light. Accommodation is efficient upon the near point.
• For young children, the near point might be as close as 7.5 cm.
• The least distance of distinct vision for the normal eye is around 25 cm.

2) Accommodation: This is the capability of the eye to focus both near and far objects on the retina via the action of the ciliary muscle through which the focal length of the lens is modified.

3) Binocular vision: It is the combination of the two over-lapping views of the object view by both eyes in such a manner as to make the right sense of distance and depth. Through binocular vision we get a correct viewpoint of an object.

4) Persistence of vision: A clear image made on the retina provides a sensation of vision that remains for a short although definite time.

The retention of vision of the image is termed as the persistence of vision. When a light thicker at an extremely short interval of around ten times per second, it comes into view to the eye as a continuous source of light owing to the persistence of vision. This fact is made use of in the production and representation of motion pictures. A fast succession of separate pictures cast on the screen appears to encompass continuity and can illustrate motion. When the speed of the successive pictures is decreased, the continuity is broken and the moment in the series becomes jerky or a thickening effect noticed.

Defects of Vision and their Corrections:

The main defects of vision that can be corrected by means of lenses are short sightedness (or myopia), long sightedness (or hyper myopia), loss of accommodation (presbyopia) and astigmatism. Such eye defects are corrected by the use of appropriate spectacles or by contact lenses that are placed to fit closely on the cornea.

1) Short Sightedness (Myopia):

Meaning: This is the capability of a person to view near objects clearly however not distant objects. This eye defect is termed as short- sightedness.

Cause: This is mainly caused by the person's eye ball being too long and so focus far-off object in front of the retina. The far point for the eye is much closer than the normal eye.

Correction: A short sighted person must wear a concave (or diverging) spectacle lens. This spectacle lens (or concave) is utilized to form a virtual image of a distant object at person's far point.

Parallel rays from a far-away object appear to diverge from a far point (that is, the principal focus of the spectacle lens) and make them come out to come from a near distance. The short-sighted person has no problem of seeing near object closer to the eye than 25 cm as by the spectacle, the near point is slightly further away from eye.

2) Long-Sight (Hyper myopia):

Meaning: This is the ability of a person to see distant object clearly however not near object. General illustration is those who need glasses to read though not to see far-away object.

Cause: This is mainly caused by the person's eye ball being two short or eye lens being too thin or the optical system of the eye being too weak so that the rays from the normal near point (25 cm) are brought to focus beyond, rather than on, the retina. That is, rays from near objects focus behind the retina.

Correction: A convex (or converging) lens is employed for the correction of long-sight. The focal length must be such that it would generate a virtual image of an object placed 25 cm away at the person's near point.

3) Loss of Accommodation (Presbyopia):

Meaning: It is the loss of elasticity of the eye-lens. That is, the eye-lens tends to become inelastic and not capable to accommodate. The far point generally approaches the eye whereas the near point recedes.

Cause: This is mainly caused by means of increasing age which makes the eye-lens to become inelastic and not capable to accommodate.

Correction: It needs two pairs for its correction. A pair of concave mirror for viewing far-away objects and a convex pair for viewing the close objects. The two pairs might be joined in one frame by the top and bottom parts having dissimilar powers (that is, bifocal spectacles).

4) Astigmatism:

Meaning: This is when the focusing power of the eye is diverse in different planes. The horizontal lines might come out in focus whereas the vertical lines are not seen clearly.

Cause: This is mainly caused due to the deformation of the curvatures of the cornea or of the eye-lens.

Correction: This is corrected through shaping the spectacle lens so as to have dissimilar curvatures in various directions.

Similarities and differences of Human Eye and Camera:

The similarities:

a) The human eye is saturated by means of black pigments within as the camera consists of light tight box painted black within.

b) The pupil of eye serves up the similar function as the aperture of the camera.

c) Both the human eye and camera include converging lens to focus rays from the external object.

d) Both contain light sensitive materials on which the rays are focused; the retina in the eye and the film in the camera.

e) The iris in the human eye serves up the similar function as the diaphram in the Camera, to control the amount of light entering the eye (or camera).

The differences:

a) The human eye consists of the power of accommodation. That is, can differ its lens focal length whereas the focal length of the camera is fixed.

b) The distance between the lens and retina is fixed in the human eye. In case of camera, the distance between the lens and the film can be differed.

c) The eye can experience from the defect of vision dissimilar the camera.

d) The eye is a biological organ whereas the camera is a mechanical tool, leading to other differences.

Simple and Compound Microscopes:

Simple Microscope or Magnifying Glass:

The lens system categorization splits the microscope into simple or compound microscopes. A simple microscope comprises of a single lens or some lenses grouped in one unit and are merely employed to make bigger an object. The lens system ranges from double convex to two plano-convex lenses. Illustrations of simple microscopes comprise reading glasses, pocket magnifiers and jewelry eyepieces.

Magnification of the object generated by the lens is given by the formula:

M = 1 - D/f

M = 1 + D/F

Here, M is the angular magnification, D is the least distance of distinct vision and F is the focal length of the lens.

Compound Microscope:

The compound microscope comprises necessarily of two or more double convex lenses fixed in the two extremities of a hollow cylinder. The lower lens (closest to the object) is termed as the objective; the upper lens (closest to the eye of the observer) is the eyepiece. The cylinder is build up upright on a screw device, that lets it to be raised or lowered till the object is in focus, that is, until a clear image is made. If an object is in focus, a real, inverted image is made by the lower lens at a point within the principal focus of the upper lens. This image serves up as an 'object' for the upper lens that generates the other image larger still (however virtual) and visible to the eye of the observer.

The Telescope:

The telescope is a device for viewing distant objects like the planets and stars. All telescopes comprises of objective convex lens or concave mirror of long focal length as the distance of the objects to be viewed and an eyepiece lens of short focal length for generating magnified image.

1) Astronomical Telescope:

The astronomical telescope makes utilization of two positive lenses: the objective that forms the image of a distant object at its focal length and the eyepiece that acts as a simple magnifier with which to view the image made by the objective. Its length is equivalent to the sum of the focal lengths of the objective and eye-piece, giving an inverted image.

The astronomical telescope can be employed for terrestrial viewing, however seeing the image upside down is a definite problem.

2) Terrestrial Telescope:

This is a customized astronomical telescope for viewing distant objects on the surface of earth. The basic difference between the terrestrial telescope and the astronomical telescope is that a convex lens is placed in between the objective and the eyepiece so that the final image is in erect position, however having the size unchanged is achieved.

3) Galilean Telescope:

Galilean telescope, an instrument for viewing the far-away objects, named after the great Italian scientist Galileo Galilei, who first made one in the year 1609. With it, he discovered Jupiter's four biggest satellites, spots on the Sun, stages of Venus, and valleys-hills on the Moon. It comprises of a convergent lens as objective (that is, the lens which makes the image); and its eyepiece (or ocular), put in front of the focus, is a divergent lens. An upright image is generated. This simple refracting telescope is still employed in modern opera glasses that are low-powered binoculars.

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