Focal Length of Converging Lens: 10.03 cm

[whitehorsey]

1. When an object 5.0 cm tall is placed 12 cm from a converging lens, an image is formed on the same side of the lens as the object but the image is 61 cm away from the lens. What is the focal length of the lens?



2. 1/f = 1/d_o + 1/d_i



3. 1/f = 1/d_o + 1/d_i
= 1/12 + 1/61
= 10.03 cm

I'm not sure if this is right.

 

[nickjer]

Be careful with the signs of the distances. If you place the object on the left of the lens then you have d₀ = +12 cm. But you also have an image on the left side of the lens. So check the sign of the image.

 

[whitehorsey]

Be careful with the signs of the distances. If you place the object on the left of the lens then you have d₀ = +12 cm. But you also have an image on the left side of the lens. So check the sign of the image.

oh ok thank you!