An object placed 12 cm from a concave mirror produces a real image 8.0 cm from the mirror.If the object is now moved to a new position 15.0 cm from the mirror,where is the new image located as measured from the mirror?
A) 6.5 cm
B) 14.6 cm
C) 7.1 cm
D) 3.0 cm

Question

Quizplus · Accepted Answer

Using the mirror formula, 
1/v - 1/u = 1/f
where, 
v = image distance
u = object distance
f = focal length

Given, u = 12 cm, v = 8 cm
1/8 - 1/12 = 1/f
f = -24 cm (negative sign indicates concave mirror)

Now, when the object is moved to a new position u = 15 cm
Using the same formula, 
1/v - 1/15 = 1/-24
v = 7.1 cm (approx)

Therefore, the new image is located at a distance of 7.1 cm from the mirror. 
Hence, the answer is (C).

An Object Placed 12 Cm from a Concave Mirror Produces