Quiz
Quiz 1. When light passing through a lens, the light is bent, causing the rays of light to diverge. The type of lens is a ...
a. convex lens
b. concave lens
c. optic lens
d. diamond prism lens
Answer) b.
A lens that causes light rays initially parallel to the central axis to converge is (reasonably) called a concave (converging) lens
Quiz 2. The lens of the human eye is a convex lens. That means that when it takes in light from an object, it refracts the light rays, by focussing them on the retina. If the eye is too long, the image will form in front of the retina. This condition is called ...
a. retina dysfunction
b. optical illusion
c. near-sightedness
d. far-sightedness
Answer) c.
Near-sightedness is when people have trouble seeing distant objects, because the object is in focus in front of the retina and then out of focus when it reaches the retina
Convex and Concave Lens Simulation
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Thin Lenses
A lens is a transparent object with two refracting surfaces whose central axes coincide. The common central axis is the central axis of the lens. When a lens is surrounded by air, light refracts from the air into the lens, crosses through the lens, and then refracts back into the air. Each refraction can change the direction of travel of the light.
A lens that causes light rays initially parallel to the central axis to converge is (reasonably) called a converging lens. If, instead, it causes such rays to diverge, the lens is a diverging lens. When an object is placed in front of a lens of either type, light rays from the object that refract into and out of the lens can produce an image of the object.
Fig 1. When rays of light pass through (a) a converging lens (thicker at the middle), they are bent inward. When they pass through (b) a diverging lens (thicker at the edge), they are bent outward.
Locating Images of Extended Objects by Drawing Rays
Fig2 (a) shows an object O outside focal point $\ F_1$ of a converging lens. We can graphically locate the image of any off-axis point on such an object (such as the tip of the arrow in Fig2 (a) by drawing a ray diagram with any two of three special rays through the point.These special rays, chosen from all those that pass through the lens to form the image, are the following:
1. A ray that is initially parallel to the central axis of the lens will pass through focal point $\ F_2$ (ray 1 in Fig2 (a).
2. A ray that initially passes through focal point $\ F_1$ will emerge from the lens parallel to the central axis (ray 2 in Fig2 (a).
3. A ray that is initially directed toward the center of the lens will emerge from the lens with no change in its direction (ray 3 in Fig2 (a). because the ray encounters the two sides of the lens where they are almost parallel.
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The image of the point is located where the rays intersect on the far side of the lens. The image of the object is found by locating the images of two or more of its points. Fig2 (b) shows how the extensions of the three special rays can be used to locate the image of an object placed inside focal point $\ F_1$ of a converging lens.
Note that the description of ray 2 requires modification (it is now a ray whose backward extension passes through $\ F_1$).
You need to modify the descriptions of rays 1 and 2 to use them to locate an image placed (anywhere) in front of a diverging lens. In Fig2 (c), for example, we find the point where ray 3 intersects the backward extensions of rays 1 and 2.
Images Created by Converging Lenses : Ray diagrams
Diverging lenses produce virtual images from real objects
A diverging lens creates a virtual image of a real object placed anywhere with respect to the lens. The image is upright, and the magnification is always less than one; that is, the image size is reduced. Additionally, the image appears inside the focal point for any placement of the real object.
Fig3. The image created by a diverging lens is always a virtual, smaller image.
The ray diagram shown in Fig3. for diverging lenses was created using the rules given in Table. The first ray, parallel to the axis, appears to come from the focal point on the same side of the lens as the object. This ray is indicated by the oblique dashed line. The second ray passes through the center of the lens and is not refracted. The third ray is drawn as if it were going to the focal point in back of the lens. As this ray passes through the lens, it is refracted parallel to the principal axis and must be extended backward, as shown by the dashed line. The location of the tip of the image is the point at which the three rays appear to have originated.
Images Created by Converging Lenses : Ray diagrams
Diverging lenses produce virtual images from real objects
A diverging lens creates a virtual image of a real object placed anywhere with respect to the lens. The image is upright, and the magnification is always less than one; that is, the image size is reduced. Additionally, the image appears inside the focal point for any placement of the real object.
Fig3. The image created by a diverging lens is always a virtual, smaller image.
The ray diagram shown in Fig3. for diverging lenses was created using the rules given in Table. The first ray, parallel to the axis, appears to come from the focal point on the same side of the lens as the object. This ray is indicated by the oblique dashed line. The second ray passes through the center of the lens and is not refracted. The third ray is drawn as if it were going to the focal point in back of the lens. As this ray passes through the lens, it is refracted parallel to the principal axis and must be extended backward, as shown by the dashed line. The location of the tip of the image is the point at which the three rays appear to have originated.
Related Videos : Convex and Concave Lens Experiment
Following video is experiment of convex and concave lens