Give students a time limit for their responses.Present the topic to students and ask them to create their list.Review your list, looking for any items you may have left out.Based on the time and item limit set, test it out by making a list of words and phrases you can recall that are related to and subsumed by your heading.Write that word or phrase at the top of a sheet of paper as a heading of related terms critical to understanding that topic.Select a topic or concept that the class has just studied or will study and describe it in a word or phrase.Use the results to gauge the best starting point, make midpoint corrections, or measure the class’s progress in learning one specific element of the course content. Decide when the activity will take place (before, during, or after a relevant lesson).Conversely, it can focus rays directed at the focal point that is behind the mirror towards the focal point that is in front of the mirror as in a Cassegrain telescope.The following workflow is meant as guidance for how you can facilitate a Focused Listing learning activity within a classroom. A convex hyperbolic mirror will reflect rays emanating from the focal point in front of the mirror as if they were emanating from the focal point behind the mirror. A convex elliptical mirror will reflect light directed towards one focus as if it were radiating from the other focus, both of which are behind the mirror. A convex parabolic mirror will reflect a beam of collimated light to make it appear as if it were radiating from the focal point, or conversely, reflect rays directed toward the focus as a collimated beam. Instead, the focus is the point from which the light appears to be emanating, after it travels through the lens or reflects from the mirror. The focus of a hyperbolic mirror is either of two points which have the property that light from one is reflected as if it came from the other.ĭiverging (negative) lenses and convex mirrors do not focus a collimated beam to a point.Elliptical mirrors have two focal points: light that passes through one of these before striking the mirror is reflected such that it passes through the other.The distance in air from the lens or mirror's principal plane to the focus is called the focal length. Since light can pass through a lens in either direction, a lens has two focal points – one on each side. For a lens, or a spherical or parabolic mirror, it is a point onto which collimated light parallel to the axis is focused.The border between these is sometimes defined using a " circle of confusion" criterion.Ī principal focus or focal point is a special focus: Aberrations tend to worsen as the aperture diameter increases, while the Airy circle is smallest for large apertures.Īn image, or image point or region, is in focus if light from object points is converged almost as much as possible in the image, and out of focus if light is not well converged. In the absence of significant aberrations, the smallest possible blur circle is the Airy disc, which is caused by diffraction from the optical system's aperture. This non-ideal focusing may be caused by aberrations of the imaging optics. Although the focus is conceptually a point, physically the focus has a spatial extent, called the blur circle. In geometrical optics, a focus, also called an image point, is a point where light rays originating from a point on the object converge. Text on a page that is partially in focus, but mostly not in varying degrees
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