The lens formula relating the image distance,p,to the focal length,f,and object distance,s,is The magnification of a lens is
-A magnifying glass with focal length 15 cm is placed 10 cm above a stamp.The magnification of the magnifying glass in is
A)+3.
B)-3.
C)+15.
D)-15.
E)+30.

Question

The lens formula relating the image distance,p,to the focal length,f,and object distance,s,is  The magnification of a lens is 
-A magnifying glass with focal length 15 cm is placed 10 cm above a stamp.The magnification of the magnifying glass in is
A)+3. 
B)-3. 
C)+15. 
D)-15. 
E)+30.

Quizplus · Accepted Answer

Using the lens formula: 1/p + 1/s = 1/f 
We know f = 15 cm and s = 10 cm 
Solving for p:

1/p + 1/10 = 1/15

1/p = 1/15 - 1/10

1/p = 1/30

p = 30 cm

Using the magnification formula: m = -p/s

m = -30/10

m = -3

The negative sign indicates that the image is inverted. Therefore, the magnification of the magnifying glass is -3. Answer choice A is correct.

The Lens Formula Relating the Image Distance,p,to the Focal Length,f,and