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- Dictionaryfocus/ˈfəʊkəs/
noun
- 1. the centre of interest or activity: "this generation has made the environment a focus of attention" Similar
- 2. the state or quality of having or producing clear visual definition: "his face is rather out of focus" Similar
verb
- 1. adapt to the prevailing level of light and become able to see clearly: "try to focus on a stationary object"
- 2. pay particular attention to: "the study will focus on a number of areas in Wales"
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An object is placed beyond the principal focus at a distance of 9 cm from it in front of a concave mirror on the principal axis. The image is formed beyond the principal focus at a distance of 16 cm from the principal focus. The focal length of the mirror is
Define focus. Question. Define focus . Open in App. Solution. A focus also called an image point, is the ...
Focus: It is the point of the principal axis at which the rays parallel to the principal axis meet (concave mirror) or appear to meet (convex mirror) after reflection. It is represented by F. Focal Length: The distance between the pole and the principal focus of a spherical mirror is called the focal length.
The principal focus or focal Point of a spherical mirror is on the axis of a mirror or lens where after reflection or refraction rays of light parallel to the axis converge or begin to converge. If a bunch of rays of light is shined straight at a concave mirror, all of those beams will be mirrored by the mirror and will all meet at one point.
Focus Incidence: When a ray passes through the focus and strikes a concave or convex mirror, the reflected ray will be parallel to the principal axis. This characteristic holds for concave and convex mirrors and is crucial in determining the path of reflected rays.
Define focus and principal focus of a lens. Derive mirror formula for a concave mirror when image formed is (i) real (ii) virtual. Also give the sign convention used.
In a spherical mirror, the distance of the object from its pole is called the object distance (u) and the distance of the image from the pole is called the image distance (v). As mentioned earlier, the distance of the principal focus from the pole is called the focal length (f). Substituting u, v, and f by following the sign convention, we get,
(c) A ray passing through the focus cuts through the principal axis of a concave mirror after reflection. (d) When an object is placed between a concave mirror and its focus, the image formed is virtual, erect and larger than the object. (e) The image formed on a cinema screen is virtual. (f) A convex mirror is used by stage artists.
The portion of a tangent to a parabola cut off between the directrix and the curve subtends a right angle at the focus. Tangents at the extremities of any focal chord intersect at right angles on the directrix. The perpendicular drawn from a focus upon any tangent of a parabola lies on the tangent at the vertex. Four Common Forms of a Parabola
When a ray, parallel to the principal axis strikes concave or convex lenses, the reflected ray passes through a focus on the principal axis. When a ray, passing through focus strikes concave or convex lenses, the reflected ray will pass parallel to the principal axis. Watch the video and learn more about image formation by lenses
