What is the right formula for a convex lens if the image is virtual? 1/d_0 + 1/d

Question

What is the right formula for a convex lens if the image is virtual? 1/d_0 + 1/d_i = 1/f -1/d_0 + 1/d_i = -1/f 1/d_0 -1/d_i = 1/f 1/d_0 -1/d_i = -1/f -1/d_0 +1/d_i = 1/f A converging lens has a focal length of f = 20 cm. If an object is placed 38 cm from the lens, where will the image be formed? Express the answer in cm (numerical value only) with one decimal place. Where will the image be located, if the object is infinitely far from a converging lens with focal length f? On the focal plane on the same side of the lens as the object. On the focal the plane on the other side of the lens. Infinity far, on the other side of the lens. At a distance of 2f on the other side of the lens. A converging lens has a focal length of f = 26 cm. An object is placed 36 cm from the lens. Find the size of the image in cm if the object has a height of 7 cm. Express the answer (numerical value only) with one decimal place.

Explanation / Answer

1. 1/f = 1/di + 1/do

if image is virtual then di will be negative.

di -> -di

1/f = 1/do - 1/di

2. do = 38 cm

f = 20 cm

1/f = 1/do + 1/di

1/20 = 1/38 + 1/di

di = 42.22 cm

3. on the focal plane on the other side of lens.

4. 1/26 = 1/36 + 1/di

di = 93.6 cm

m = - di/do = hi/ho

- 93.5 / 36 = hi / 7

hi = - 18.2 cm

negative sign indicates that image will be inverted.

image height = 18.2 cm   

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