Question

2. A concave lens of focal length 15 cm forms an image 10 cm from the lens. How far is the object placed from the lens? Draw the ray diagram.​

Answer 1

Answer:

iven: f=−15

           v=−10

From mirror formula,  

v

1

​

−  

u

1

​

=  

f

1

​

 

                                     

−10

1

​

−  

u

1

​

=  

−15

1

​

 

                                     

u

1

​

=  

15

1

​

−  

10

1

​

 

                                   u=−30 cm

Explanation:

Answer 2

Answer:

Focal length (f ) = -15 cm

Distance of image (v) = -10 cm

\(\frac{1}{v} – \frac{1}{u} = \frac{1}{f}\)

1/u = -(1/10) – (1/- 15)

1/u =1/15 – 1/10

1/u = -0.033

u = -30 cm

So, the object is placed 30 cm away from the concave lens.

Ray diagram: