A deplorable kid is attempting to burn ants with a magnifying glass and hasn\'t

Question

A deplorable kid is attempting to burn ants with a magnifying glass and hasn't succeeded in finding the right distance yet. The magnifying glass has a focal length of 20.7 cm, and the kid holds it 10.4 cm away from the ant. If the kid's eye is 18.0 cm away from the magnifying glass on the other side from the ant :

(a) How far away is the ant actually from the kid's eye?

(b) How many times larger is the image of the ant than the ant itself?

(c) How far away does the ant appear to be from the kid's eye?

Draw a ray trace diagram of the magnifying glass and ant. Include the following:

1. The 3 principle rays

2. The optical axis

3. The object and image location and size

4. Draw clearly whether the images is upright or inverted

5. State whether it is real or virtual

Explanation / Answer

distance between ant and eyes = distance between lens and eyes + distance between ant and lens

distance between ant and eye = 18 + 10.4

distance between ant and eye = 28.4 cm

magnification = -distance of image / distance of object

magnification = -18 / 10.4

magnification = 1.73

image of ant will be 1.73 time larger than ant itself

1 / f = 1 / v + 1 / u

1 / 20.7 = 1 / 18 + 1 / u

u = -138 cm

ant appears to be 138 - 18 cm from eye

ant appears to be 120 cm from eye

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