name five instruments which rely on lenses to work
Answers
Answer:
The Magnifying Glass
A magnifying glass is a convex lens that lets the observer see a larger image of the object being observed.
LEARNING OBJECTIVES
KEY TAKEAWAYS
Key Points
The magnification of a magnifying glass depends upon where it is placed between the user’s eye and the object being viewed and upon the total distance between eye and object.
The magnifying power is the ratio of the sizes of the images formed on the user’s retina with and without the lens.
The highest magnifying power is obtained by putting the lens very close to the eye and moving both the eye and the lens together to obtain the best focus.
Key Terms
lens: an object, usually made of glass, that focuses or defocuses the light that passes through it
diopter: a unit of measure of the power of a lens or mirror, equal to the reciprocal of its focal length in meters. Myopia is diagnosed and measured in diopters
convex: curved or bowed outward like the outside of a bowl or sphere or circle
A magnifying glass is a convex lens that lets the observer see a larger image of the object under observation. The lens is usually mounted in a frame with a handle, as shown below.
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Magnifying Glass: A magnifying glass is a convex lens that lets the observer see a larger image of the object under observation.
The magnification of a magnifying glass depends upon where the instrument is placed between the user’s eye and the object being viewed and upon the total distance between eye and object. The magnifying power is the ratio of the sizes of the images formed on the user’s retina with and without the magnifying glass. When not using the lens, the user would typically bring the object as close to the eye as possible without it becoming blurry. (This point, known as the near point, varies with age. In a young child its distance can be as short as five centimeters, while in an elderly person its distance may be as long as one or two meters. ) Magnifiers are typically characterized using a “standard” value of 0.25m.
The highest magnifying power is obtained by putting the lens very close to the eye and moving both the eye and the lens together to obtain the best focus. When the lens is used this way, the magnifying power can be found with the following equation:
[latex]\text{MP}_{0} = \frac{1}{4}\cdot \Phi +1[/latex]
where [latex]\Phi[/latex] = optical power. When the magnifying glass is held close to the object and the eye is moved away, the magnifying power is approximated by:
[latex]\text{MP}_{0} = \frac{1}{4}\cdot \Phi[/latex]
Typical magnifying glasses have a focal length of 25cm and an optical power of four diopters. This type of glass would be sold as a 2x magnifier, but a typical observer would see about one to two times magnification depending on the lens position.
The earliest evidence of a magnifying device was Aristophanes’s “lens” from 424 BC, a glass globe filled with water. (Seneca wrote that it could be used to read letters “no matter how small or dim.”) Roger Bacon described the properties of magnifying glasses in the 13th century, and eyeglasses were also developed in 13th-century Italy.
The Camera
Cameras are optical devices that allow a user to record an image of an object, either on photo paper or digitally.
LEARNING OBJECTIVES
KEY TAKEAWAYS
Key Points
Cameras work very similarly to how the human eye works. The iris is similar to the lens; the pupil is similar to the aperture; and the eyelid is similar to the shutter.
Cameras are a modern evolution of the camera obscura. The camera obscura was a device used to project images.
The most important part of a camera is the lens, which allows the image to be magnified and focused. This can be done manually on some cameras and automatically on newer cameras.
Movie cameras work by taking many pictures each second and then showing each image in order very quickly to give the effect that the pictures are moving. This is where the name “movie” comes from.
Key Terms
shutter speed: The duration of time for which the shutter of a camera remains open when exposing photographic film or other photosensitive material to light for the purpose of recording an image
