# What equation should I use Callum is examining a square stamp of side 3.16 cm with a magnifying glass of [Solved] so the ratio ( angular magnification ) is ( x/2) / ( x/25) = 25/2 = 12.5

According to wikipedia the refractive power is the reciprocal of the focal length of the lens.
So 46 Dioptre has a focal length f = 1/46 m

Now we can use the formula 1/ Do 1/ Di = 1/f
Di is given as 0.243 m
so 1/Do 1/ 0.243 = 46
1/Do = 46 1/0.243 = 42
Do = 1/42 = 0.024 or 2.4 cm from the lens.

So the size of the image is object size * magnification
= 3.16 * 24.3/2 = 38.4 cm

OK so I reread my own answer. The image is on the WRONG side of the lens so Di is negative.
therefore 1/Do 1.0.243 = 46
1/Do = 46 1/0.243 = 50.11
D= 0.020 m

Now for part C
As the ray which passes through the centre of the lens is unbent then the magnification is Di/Do
= 24.3/2
= 12.2 approx

So the size of the image is object size * magnification
= 3.16 * 24.3/2 = 38.4 cm

Originally the stamp had a height of x at 25 cm without the lens, and now the stamp can be placed at 2 cm from the lens.

Stamp Magnifier

The ray passing through the centre of the lens emerges undeflected. So the tangent of the angle when the stamp is at 2 cm is x/2
When it was at 25 cm the angle was x/25

Originally the stamp had a height of x at 25 cm without the lens, and now the stamp can be placed at 2 cm from the lens.

Sorry for my mistake earlier and I hope you get to read this new and updated answer.
Andrew

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So the size of the image is object size * magnification
= 3.16 * 24.3/2 = 38.4 cm

This post is last updated on hrtanswers.com at Date : 1st of September – 2022