The power of the lens is 2 diopter means that this lens has a focal length of 1/2 meter.
The focal length = 1 ÷ ( the number of diopters)
If one's glass prescription shows that the power of the lens is 2 diopter it means that the person is far-sighted. It means if a person needs to see something which is quite distant then his eyes need extra lens power to focus on it. Moreover, if there's a sign convention it means '+' indicates a convex lens and '-' concave lens. Also in-camera close up lens are also measured in terms of diopter.
I hope this answer helps.
To learn more about lenses,
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The normal force would be the opposing and equal force to gravity ... that is why the box isn't floating or going through the ground ... this is Newton's third law of motion
Answer:2 m right
Explanation:
Given
First child is sitting 1 m left from Pivot point
Mass of second child is half of first
Let mass of first child be m
Second child 
In order to balance see saw torque must be zero about pivot
x=2 m right from pivot point
