Q27 of 36 Page 283

Find the position of an object which when placed in front of a concave mirror of focal length 20 cm produces a virtual image twice the size of the object.

Given,

Focal length of concave mirror = 20 cm


If H is the height then,


H image = 2× H object




Magnification = 2




v = -2u . . . . . . equation 1


We know that mirror formula is:



Substituting the given values





2u = 20


U = 10 cm


So the position of the object is 10 cm to the left of the mirror


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25

An object is placed perpendicular to the principal axis of a convex lens of focal length 18 cm. The distance of the object from the lens is 27 cm. Find the position and nature of the image formed.

 26

Draw the ray diagram to show the formation of image by a concave mirror of focal length 15 cm for the following positions of object. (Diagrams may not be drawn to the scale.)

Indicate is placed at 30 cm from mirror.


a. object is placed at 30 cm from mirror.


b. object is placed at 10 cm form the mirror.

 28

An object 2 cm in size is placed 20 cm in front of a concave mirror of focal length 10 cm. Find the distance from u the mirror at which a screen should be placed in order to obtain sharp image. What will be the size and nature of the image formed?

 29

When an object is placed at a distance of 60 cm from a convex mirror the magnification produced is 1/2. Where should the object be placed to get a magnification of 1/3.