Question

An object is placed 60 cm from a screen. Where should you place a convex lens of focal length 15 cm to get the image of the object on the screen?

Answer 1

Answer on Question #75516, Physics / Optics

An object is placed 60 cm from a screen. Where should you place a convex lens of focal length 15 cm to get the image of the object on the screen?

Answer:

Let: $F$ – focal length, $f$ – distance from image to lens, $d$ – distance from object to lens

According to thin lens formula:

$$\frac{1}{F} = \frac{1}{f} + \frac{1}{d} = \frac{1}{0.15}$$

Also, in our case, distance from object to screen is fixed: $f + d = 0.6$

So, we have:

$$\begin{cases} - \frac{1}{15} = \frac{1}{f} + \frac{1}{d} \\ f + d = 0.6 \end{cases}$$

From this, we find $f, d$:

$$\begin{array}{l} f = 0.3m \\ d = 0.3m \\ \end{array}$$

So, you have to place a lens exactly in the middle.

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