Question

The focal length of a convex lens is 10cm, find the position of image when the object is placed at a distance of 30cm from a convex lens.

Answer 1

Answer on Question #64048, Physics / Optics

The focal length of a convex lens is $10\mathrm{cm}$, find the position of image when the object is placed at a distance of $30\mathrm{cm}$ from a convex lens.

Find: $d_i - ?$

Given:

$f = 10\mathrm{cm}$

$d_0 = 30\mathrm{cm}$

Solution:

If the distances from the object to the lens and from the lens to the image are $d_0$ and $d_i$ respectively, for a lens of negligible thickness, in air, the distances are related by the thin lens formula:

$$\frac {1}{d _ {0}} + \frac {1}{d _ {i}} = \frac {1}{f} (1),$$

where $f$ is focal length of a convex lens

Of (1) $\Rightarrow d_{i} = \frac{f d_{0}}{d_{0} - f}$ (2)

Of (2) $\Rightarrow d_{i} = 15\mathrm{cm}$

Answer:

15 cm

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