An object is placed before a concave lens of focal length 12cm. The size of the image formed by the lens is half the size of the object. Calculate the distance.

Asked by rana.vedant01 | 29th May, 2020, 04:18: PM

Expert Answer:

f = - 12 cm (focal length of concave lens)  
m = + 0.5 ...(image formed by concave lens is virtual, erect and diminished) 
 
m space equals v over u
0.5 equals v over u
v space equals space 0.5 space u space

B y space l e n s space f o r m u l a comma space
1 over v minus 1 over u equals 1 over f
fraction numerator 1 over denominator negative 12 end fraction equals space fraction numerator 1 over denominator 0.5 u end fraction minus 1 over u space
fraction numerator 1 over denominator negative 12 end fraction equals fraction numerator u minus 0.5 space u over denominator 0.5 u squared end fraction space equals space fraction numerator 0.5 u over denominator 0.5 u squared end fraction space equals 1 over u
u space equals negative 12 space c m space
 
Thus, object distance is 12 cm to the left side of concave lens. 

Answered by Shiwani Sawant | 29th May, 2020, 05:51: PM