Image Formation by Spherical Mirrors through Activities

Image Formation by Spherical Mirrors Image Formation by Spherical Mirrors

We have studied about the image formation by plane mirrors. We also know the nature, position and relative size of the images formed by them. How How about about the the images images formed formed by by spherical spherical mirrors? mirrors? How mirror Are Are they size? How can mirror for Are the they enlarged, size? can we for different the images enlarged, diminished we locate different positions images real locate the the image positions of real or diminished or image formed of the or virtual? formed by the object? by a a concave object? concave virtual? Are or have have the the same same We shall explore this with an Activity.

Activity Activity We have already learnt a way of determining the focal length of a concave mirror. We have seen that the sharp bright spot of light you got on the paper is, in fact, the image of the Sun. It was a tiny, real, inverted image.We got the approximate focal length of the concave mirror by measuring the distance of the image from the mirror . Take a concave mirror. Find out its approximate focal length. Note down the value of focal length. Mark a line on a Table with a chalk. Place the concave mirror on a stand. Place the stand over the line such that its pole lies over the line. Draw with a chalk two more lines parallel to the previous line such that the distance between any two successive lines is equal to the focal length of the mirror. These lines will now correspond to the positions of the points P, F and C, respectively. Remember For a spherical mirror of small aperture, the principal focus F lies mid-way between the pole P and the centre of curvature C.

Keep paper image Observe with just Keep a a bright paper screen image of Observe the with respect just beyond bright object, screen and of the the image respect to beyond C, object, say and move the candle image carefully to the C, (b) say a a burning move it it in candle flame carefully. . Note the object (b) at burning candle, in front flame on Note down object size at C, candle, at of the at a a position the mirror position far till you far beyond you obtain beyond C C. . Place obtain a a sharp Place a a bright front of on it it. . mirror till sharp bright down its Repeat the and C, its nature, the activity C, (d) nature, position activity by (d) at position and by placing at F, F, and and relative the candle between P P and relative size candle (a) and F F. . size (a) size. . Repeat (c) between placing the and (e) C, (c) between F F and (e) between In In one one of of the the cases, cases, you you may may not not get get the the image image on on the the screen screen. . Identify image Identify the image in the position in the position of the mirror of the itself. . Note the object Note down object in down and in such and tabulate such a a case tabulate your case. . Then, your observations Then, look observations look for for its its virtual virtual mirror itself

We will see in the above Activity that We will see in the above Activity that the nature, position and size of the image formed by a concave mirror depends object The image formed is real object. It is found to be a virtual position. depends on the position and C C. position of of the the object in relation to points P, P, F F and real for some positions of the virtual image for a certain other The image is either magnified same magnified, reduced reduced or has the same size size, depending on the position of the object

Representation of Images Spherical Mirrors Representation of Images Formed by Spherical Mirrors Using Formed by Using Ray Diagrams Ray Diagrams

To the number considered consider the it it is is easy from To construct the image number of considered. . However, consider only the ray easy to from the construct the image of of rays the ray of an rays emanating However, it it is is more only two ray diagram to know the mirror in order an arbitrarily from a a point more convenient for the These rays know their mirror. . ray diagrams, an object, emanating from order to arbitrarily large point could convenient to the sake rays are their directions diagrams, in object, an to locate large could be locate be to of that two rays, rays, for sake of are so after reflection of clarity so chosen reflection clarity of chosen that diagram. . These directions after The give The intersection give the intersection of the position of at of image at least image of least two of the two reflected the point reflected rays point object rays position of object. .

i) i) A A ray reflection case from ray parallel reflection, , will case of from the parallel to will pass of a a concave the focus to the through the mirror or in case the principal the principal or appear case of principal axis principal focus appear to of a a convex axis, , after focus in to diverge mirror. . after in diverge pass through concave mirror focus in convex mirror

(ii) focus is is directed of emerge (ii) A A ray focus of directed towards of a a convex emerge parallel ray passing of a a concave towards the convex mirror parallel to passing through concave mirror through the mirror or the principal mirror, , after to the the principal or a a ray principal focus after reflection, the principal principal ray which focus reflection, will principal axis which will axis. .

(iii) of the reflection, (iii) A A ray of a a concave the centre reflection, is is reflected ray passing concave mirror centre of passing through mirror or of curvature reflected back through the or directed curvature of back along the centre directed in of a a convex along the centre of in the convex mirror the same of curvature the direction mirror, , after same path curvature direction of of after path. .

(iv) towards concave obliquely the ( (point axis iv) A A ray towards a a point concave mirror obliquely. . The the laws point P), axis ray incident point P P (pole mirror or The incident laws of P), making incident obliquely obliquely to (pole of or a a convex incident and of reflection making equal to the of the convex mirror and reflected at the equal angles the principal the mirror mirror is is reflected reflected rays the point angles with principal axis mirror), ), on reflected rays follow point of with the axis, , on the the follow incidence the principal reflection at of incidence principal

Real, inverted and highly diminished image is formed at focus

Concave mirrors are commonly used in torches, search-lights and vehicles headlights to get powerful parallel beams of light. They are often used as shaving mirrors to see a larger image of the face. The dentists use concave mirrors to see large images of the teeth of patients. Large concave mirrors are used to concentrate sunlight to produce heat in solar furnaces.

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