Phosphor burn-in is particularly prevalent with monochromatic CRT screens, such as the amber or green monochrome monitors common on older computer systems and dumb terminal stations. This is partly because those screens displayed mostly non-moving images, and at one intensity: fully on. Yellow screens are more susceptible than either green or white screens because the yellow phosphor is less efficient and thus requires a higher beam current. Color screens, by contrast, use three separate phosphors (red, green, and blue), mixed in varying intensities to achieve specific colors, and in typical usage patterns such as "traditional" TV viewing (non-gaming, non-converged TV usage, non-Internet browsing, broadcasts without tickers or flags, no prolonged or permanent letterboxing) are used for operations where colors and on-screen object placement approach uniformity.

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Problem 1: The radii of curvatures of a convex lens are 40cm and 50cm, calculate the focal length if the refractive index of its material is 2.1.

Magnification formulabiology

Screensavers derive their name from their original purpose, which was an active method of attempting to stave off screen burn. By ensuring that no pixel or group of pixels was left displaying a static image for extended periods of time, phosphor luminosity was preserved. Modern screensavers can turn off the screen when not in use.

Plasma displays produced until around 2007 were highly susceptible to burn-in, while LCD-type displays are rarely affected.[4] The wide variation in luminance degradation with RGB-based organic light-emitting diode (OLED)[5] will cause noticeable color drift over time (where one of the red-green-blue colors becomes more prominent). OLEDs do not need a backlight to light up; each pixel is a self-illuminating LED. The pixels on OLEDs inevitably lose their brightness over time. The longer an OLED pixel is used (illuminated), the dimmer it will appear next to a lesser-used pixel.[6]

It is defined as the distance between the optical center and the second primary focus, so that the focal length of a convex lens is positive and that of a concave lens is negative.

When a thin lens is submerged in water, its relative refractive index decreases, and therefore its focal length increases (and the lens’s power decreases).

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In the case of LCDs, the physics of burn-in are different than plasma and OLED, which develop burn-in from luminance degradation of the light-emitting pixels. For LCDs, burn-in develops in some cases because pixels permanently lose their ability to return to their relaxed state after a continued static use profile. In most typical usage profiles, this image persistence in LCD is only transient.

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Both plasma-type and LCD-type displays exhibit a similar phenomenon called transient image persistence, which is similar to screen burn but is not permanent. In the case of plasma-type displays, transient image persistence is caused by charge build-up in the pixel cells (not cumulative luminance degradation as with burn-in), which can be seen sometimes when a bright image that was set against a dark background is replaced by a dark background only; this image retention is usually released once a typical-brightness image is displayed and does not inhibit the display's typical viewing image quality.

Magnification formula for lensin terms of focal length

For the second refraction, I’ acts as a virtual object in lens medium of refractive index μ2, to produce a final image at I in surrounding medium of refractive index μ1. By using the relation among u. v. μ1, and R for refraction at a single curved (convex) surface.

Screen burn-in, image burn-in, ghost image, or shadow image, is a permanent discoloration of areas on an electronic visual display such as a cathode-ray tube (CRT) in an older computer monitor or television set. It is caused by cumulative non-uniform use of the screen.

Other examples: Apple's iPhone X and Samsung's Galaxy series both mitigate or delay the onset of burn-in by shifting the pixels every minute or so for the battery, Wi-Fi, location, and service bars. Also, parallax scrolling may be enabled for the home screen to give icons a 3D-like effect, a setting Apple refers to as "perspective zoom". AG Neovo patented Anti-burn-in technology is also using pixel shifting to activate the pixels to move by the designed time interval to prevent the burn-in effect on LCD monitors. [9]

One way to combat screen burn-in was the use of screensavers, which would move an image around to ensure that no one area of the screen remained illuminated for too long.

When the item is in front of the concave lens, the image is in front of the same object on the same side. The concave lens always produces a virtual, erect, and reduced image. Because concave lenses always generate virtual images, the magnification achieved by them is always positive and it always produces an image that is smaller than the object.

Magnification means making objects appear larger than they are. Following are the different cases to determine the magnification for different cases as:

Light is a kind of energy that can be seen with the naked eye. We observe objects and understand the world around us mostly via the use of light. Light travels in a straight path at an extremely fast speed of around 3 × 108 ms. A small light source produces a strong shadow on an opaque object. This means that the light travels in a straight line and the route is referred to as a ray of light, and a grouping of rays is referred to as a beam of light.

Modern CRT displays are less susceptible than older CRTs prior to the 1960s because they have a layer of aluminum behind the phosphor which offers some protection. The aluminum layer was provided to reflect more light from the phosphor toward the viewer. As a bonus, the aluminum layer also prevented ion burn of the phosphor and the ion trap, common to older monochrome televisions,[1] was no longer required.[2][3]

Case 1: If the magnitude of magnification is less than one, it means the image is smaller than the object. |m|<1, the image is diminished.

Magnificationof mirror

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Problem 2: A convex lens forms a real and inverted image of an object 40cm from the lens. Where will be the object placed in front of the convex lens, if the image is of the same size as the object?

Consider a thin glass lens with a refractive index of μ2 and curvature centres C1 and C2 with curvature radii R1 and R2. Let μ1 represent the refractive index of the surrounding medium. When a point object ‘O’ is maintained on-axis at a distance u from the lens, the ray OP passes through the optical centre without deviation. If the other ray OA had not been refracted along with AB by the first surface, it would have arrived at the point I’. If the second surface didn`t exist. But, due to the second surface, the ray undergoes another refraction at point B and reaches point I.

Magnification formula forconcave mirror

The image distance can be computed using the lens formula and knowledge of the object distance and focal length. The Lens formula describes the relationship between the distance of an image I the distance of an object (o), and the focal length (f) of the lens in optics. The lens formula works for both convex and concave lenses.

The most prevalent burn-in image on early televisions was said to be that of the RCA Indian-head test pattern, which would often follow the formal television station sign-off. This was due to the viewer leaving the television set on at the end of the day, which was not recommended by the television manufacturers.[citation needed]

A light ray indicates the direction of light propagation. When light strikes a surface between two transparent mediums, it reflects and refracts, causing light rays to bend. Light rays bend around the edge of obstruction as well, although the bending is relatively minimal due to the very short wavelength of light radiation. This is known as light diffraction.

We know the properties of convex lens that it is virtual and upright. Because a convex lens may create both virtual and actual pictures, the magnification produced by a convex lens can be either positive or negative. Magnification is beneficial for virtual images but detrimental for real images. i.e. Positive (+ve) for virtual image and Negative (-ve) for the real image.

Google requests that when these techniques are enabled, watch face developers do not use large blocks of pixels so that different pixels are burned in with each shift, reducing the overall wear of the pixels.[10]

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Below tabular representation indicates the magnification and nature of the image for different cases for different lenses as:

The focal length of a lens is determined by the refractive index of the lens’s material in relation to its surroundings, as determined by the lens maker’s formula.

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Magnification formula forconvexlens

It is equivalent to the image-to-object distance ratio. *** QuickLaTeX cannot compile formula: *** Error message: Error: Nothing to show, formula is empty

The lens equation is used by lens makers employ to create lenses with desired focal lengths. Lenses with varying focal lengths are employed in a variety of optical devices. The focal length of a lens is determined by the radii of curvature of two surfaces and the refractive index of the lens material.

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Magnificationof convexlensis positive or negative

With phosphor-based electronic visual displays (i.e. CRT-type computer monitors, oscilloscope screens, and plasma displays), non-uniform use of specific areas, such as prolonged display of non-moving images (text or graphics), repetitive contents in gaming graphics, or certain broadcasts with tickers and flags, can create a permanent ghost-like image of these objects or otherwise degrade image quality. This is because the phosphor compounds that emit light to produce images lose their luminance with use. This wear results in uneven light output over time, and in severe cases can create a ghost image of previous content. Even if ghost images are not recognizable, the effects of screen burn are an immediate and continual degradation of image quality.

The length of time required for noticeable screen burn to develop varies due to many factors, ranging from the quality of the phosphors employed, to the degree of non-uniformity of subpixel use. It can take as little as a few weeks for noticeable ghosting to set in, especially if the screen displays a certain image constantly and displays it continually over time, for example, a menu bar at the top or bottom of the screen. In the rare case when horizontal or vertical deflection circuits fail, all output energy is concentrated to a vertical or horizontal line on the display which causes almost instant screen burn.

Newer liquid-crystal displays (LCDs) may suffer from a phenomenon called image persistence instead, which is not permanent.

Magnification formula formirror

Case 3: If the magnitude of magnification is one, then the image is the same size as an object. |m| = 1, the image is same size as object.

This is the lens maker`s equation. The lens of any desired focal length can be produced by choosing proper values of R1, R2, μ1, μ2.

Some screensavers move around, such as those on DVD players or those on some television sets that move around paused video after a long period of inactivity.

Problem 5: An optical system uses two thin convex lenses in contact having an effective focal length of 30/4 cm. If one of the lenses has a focal length of 30cm, find the focal length of the other.

For the first refraction, the object distance is u, and the image distance is v’. By using the relation among u. v. μ1, and R for refraction at a single curved (convex) surface.

Magnificationof convexlens

Depending on the type of screen, it is sometimes possible to remedy screen burn-in through the use of remedial software and remedial devices. In the case of OLED screens on Android phones, burn-in reduction apps can display an inverted image of the navigation and status bars (which are constantly displayed and therefore the most likely elements to be burned in) to burn in an opposite pattern, resulting in a screen whose subpixels have more even luminosity and therefore less visible burn-in artifacts.[11]

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Problem 3: A concave lens of the focal length of 20cm forms an image of a needle 15 cm from the lens. How far is the needle placed from the lens?

In many cases, the use of a screensaver is impractical. Most plasma-type display manufacturers include methods for reducing the rate of burn-in by moving the image slightly,[7] which does not eliminate screen burn but can soften the edges of any ghost image that does develop.[8] Similar techniques exist for modern OLED displays. For example, manufacturers of Android Wear watches with OLED displays can request that Android Wear enable "burn protection techniques" that periodically shifts the contents of the screen by a few pixels.

Problem 4: a concave lens made of glass has a focal length of 20cm in air. Find its focal length when immersed in water. Given that the refracting index of the glass lens is 1.5 and that of in water is 4.

Using the new Cartesian sign convention, we get a positive focal length for the convex lens and a negative focal length for the concave lens.