Page 41 - Physics 10_Float

GEOMETRICAL OPTICS

followed to apply this equation for solving problems
related to mirrors.

Sign Conventions
–
Quantity When Positive (+ ) When Negative ( )

Object distance p Real object Virtual object
Image distance q Real Image Virtual image
Focal length f Concave mirror Convex mirror

Activity12.3: Take a concave mirror or a well polished spoon Physics insight
(using inside of the spoon with concave surface bulging N o t e t h a t t h e w o r d
inward). Hold it in hand towards a distant object, such as the magnification, as used in
optics, does not always mean
Sun, a building, a tree or a pole. Try to get a sharp, well-
enlargement, because the
focused image of the distant object on the wall or a screen. image could be smaller than
Measure the distance of the screen from the mirror using a the object.
metre scale. Can you find out the rough focal length of the
For your information
concave mirror? Draw the ray diagram to show the image
formation in this situation. Mirror

Object Image
Example 12.1: A convex mirror is used to reflect light from an
object placed 66 cm in front of the mirror. The focal length of
the mirror is 46 cm. Find the location of the image.
Solution: Given that, p = 66 cm and f = - 46 cm
Using mirror formula, 1 1 1 Ray diagram for the virtual
= – image formation in a plane
q f p
mirror.
1 = – 1 – 1
q 46 cm 66 cm Do you know?
1 = – 1
q 27 cm

q = – 27 cm

The negative sign indicates that the image is behind the
mirror and, therefore, is a virtual image.
Example 12.2: An object is placed 6 cm in front of a concave Convex mirrors produce
images that are smaller than
mirror that has focal length 10 cm . Determine the location of objects. This increases the
the image. view for the observer.

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