CBSE Class 10 Science 2017 · Paper 31/2/C · Question 19

Light - Reflection and Refraction 5 marks Medium

(a)Define the term “magnification” in the context of spherical mirrors. Express it in terms of object-distance ( $u$ ) and image-distance ( $v$ ). Besides size and position of image, what other two informations it provides about the image ?
(b)Draw a ray diagram to show the formation of image by a concave mirror when the object is placed in front of it between its centre of curvature and focus. What is the nature of the image formed ?

Answer

$m = \frac{h ^{'}}{h} = - \frac{v}{u}$ , and its sign shows whether the image is real or virtual, erect or inverted; (b) real, inverted, enlarged image beyond $C$ .

(a) The magnification produced by a spherical mirror is the ratio of the height of the image (

h^{'}

) to the height of the object (

h

m = \frac{h ^{'}}{h}

. In terms of the object distance and the image distance,

m = - \frac{v}{u}

. Besides the size and position of the image, the magnification tells us (1) whether the image is real or virtual and (2) whether it is erect or inverted: a negative value of

m

means the image is real and inverted, and a positive value means it is virtual and erect. (b) Ray diagram: from the top A of the object AB placed between C and F, a ray parallel to the principal axis is reflected through F, and a ray through F is reflected parallel to the principal axis; the reflected rays meet beyond C, where the image A′B′ is formed. Nature of the image: real, inverted and enlarged (magnified), formed beyond C.

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CBSE Class 10 Science 2017 · Paper 31/2/C · Question 19

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