A concave lens is a lens that possesses at least one surface that curves inwards. It is a diverging lens, meaning that it spreads out light rays that have been refracted through it. A concave lens is thinner at its centre than at its edges, and is used to correct short-sightedness (myopia).
A converging lens is used to project a real image onto a screen, as in Figure 26.28b. A piece of black tape is then placed over the upper half of the lens. The whole image will be seen. To see this, draw one ray from the top of the image through the center.
A concave lens cannot form an image two times that of the object because it always forms a diminished image.
Power of lense = 1/
focal length in meter. A concave
lens has a negative
focal length. Therefore, it is a concave
lens.
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How will you distinguish between a convex and a concave lens without touching them? If the curved surface is bulging outwards then it's convex lens and if the curved surface is curved inwards then it's concave lens.
Hence, If half part of a convex lens is covered, the focal length does not change, but the intensity of the image decreases.
A convex lens can produce the complete image of the object even though half of the lens is covered. This is because light coming from the object can be refracted from the other half of the lens. However, the intensity of light will be reduced.
A convex mirror or diverging mirror is a curved mirror in which the reflective surface bulges towards the light source. Convex mirrors reflect light outwards, therefore they are not used to focus light. The image is smaller than the object, but gets larger as the object approaches the mirror.
Every part of a lens forms a complete image. If the lower part of the lens is blackened, even then complete image will be formed but its intensity will decrease.
To draw an image we just need two refracted rays. If you cover a half of lens then it won't receive light and therefore the light rays contributing in the image formation will be less and therefore intensity (or brightness) of image will be reduced.
Convex (converging) lenses can form either real or virtual images (cases 1 and 2, respectively), whereas concave (diverging) lenses can form only virtual images (always case 3).
How does the focal length of a convex lens change if monochromatic red light is used instead of blue light? Refractive index of red light is less than the refractive index of blue light. So, the focal length of the lens will increase when red light is used.
A double convex lens, or converging lens, focuses the diverging, or blurred, light rays from a distant object by refracting (bending) the rays twice. This double bending causes the rays to converge at a focal point behind the lens so that a sharper image can be seen or photographed.
How will this image be different from the one obtained when the lens is not painted black? The image formed will still be of full size but the intensity of the image will be lesser, when the lower half of the lens is painted black.
Lenses serve to refract light at each boundary. As a ray of light enters a lens, it is refracted; and as the same ray of light exits the lens, it is refracted again. Because of the special geometric shape of a lens, the light rays are refracted such that they form images.
The power of a lens is defined as the reciprocal of the focal length. Converging (convex ) lenses have positive focal lengths, so they also have positive power values. Diverging (concave ) lenses have negative focal lengths, so they also have negative power values.
Why? Magnifying power is inversely related to the focal length of a lens: the bigger the focal length, the lower the magnifying power. The LDDV is a constant number, as it usually tends to be the same for people with good vision.
The image produced will be complete. But the image observed now will be fainter. Even when half of the mirror is covered with black paper, it would still produce a complete image but the image produced would be fainter (of lesser intensity) than the image produced when half mirror was not covered.
What is the Lens Formula? Answer: According to the convex lens equation, the lens formula is 1/f = 1/v + 1/u. It relates the focal length of a lens with the distance of an object which is placed in front of it and the image formed of that object.
Answer: Same size of image is formed by a convex lens only when the object is placed at a distance u=2f from the optical center and image is also formed at distance 2f on other side of lens.
When you cover the top half of the lens, the bottom half of the image disappears; when you cover the bottom half of the lens, the top half of the image disappears. Nothing happens in either case.
Only a concave mirror can form a real image. Plane mirror and convex mirror always form a virtual image of an object.
Now since the focal length is inversely proportional to the (μ−1), therefore the focal length will increase. Hence the focal length of the lens increases when it is immersed in the water. Hence, Option A is correct. Note: We compare the refraction from one medium to another by their refractive index.
Solution : In the convex lens the rays are converted to a point on the other side lens when the parallel rays are incident on the surface of the lens. If the central portion of the lens wrapped by black paper, full image will be form but with a less brightness.
If the plane mirror is covered with a black paper then the complete image of the object will be formed. It does not matter how much portion of the mirror is covered. But the intensity of the image of the object will be reduced. As the reflected rays will be less.
