The height of an image is three times that of the object when placed in front of a concave mirror of focal length 15 cm.What are the two possible locations of the object?
SAMPLE ANSWER 12C Distances may be left in cm rather than converting to SI units, therefore v 15 cm.
m v uQ3 v
If the image is real:
1 f 1
u 1 15 3
3u 60 1
v Q 1 3u 1 u 20 cm 3u f 1 u 1 3u uQv 3u If the image is virtual:
1 f 1
u 1 15 3
3u 30 1
v Q 1 3u 1 u 10 cm The two possible locations of the object are 20 cm and 10 cm in front of the mirror. EXERCISE 12.1 SPHERICAL MIRRORS
Q1 An object is placed 40 cm in front of a concave mirror of focal length 15 cm. Find the position, nature and magni- fication of the image.
Q2 An object 3 cm high is placed 20 cm in front of a concave mirror of focal length 25 cm.What is the image height? Q3 An object is placed 12 cm in front of a convex mirror of focal length 20 cm. Find the position, nature and magnifi- cation of the image.
Q4 The height of an image is four times that of the object when placed in front of a concave mirror of focal length 24 cm.What are the two possible locations of the object?
Q5 An object that is 4 cm high produces an image 2 cm high when placed 15 cm in front of a spherical mirror.What type of mirror would it be if the image is (i) real and (ii) virtual? Calculate the focal length in each case.
