Math Is Fun Forum

Adam1980

Guest

Optical area

I'm trying to work out the 'optical' area made up of strands of fibre optics. Each fibre is  0.85mm and I have 100 of them.

I already have an equation of 100 x 0.85 x 0.85 x 3.14 / 4 = 56.716

What I would like to know is:

a) Why do you devide by 4??? (is this something to do with a quadratic circle????)

b) The reason you x 0.85 twice???? Because if it were 1 you would immediatley x 3.14

Many thanks

mathsyperson

Moderator

Registered: 2005-06-22

Posts: 4,900

Re: Optical area

The formula for the area of a circle is πr², where r is its radius.

0.85 is the diameter, which is double the radius. So the formula is actually π x (0.85/2)², but the 0.85² has been split into two and the two 2's have been combined to make a division by 4. Hopefully that makes sense.

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Why did the vector cross the road?
It wanted to be normal.