Question

Help me to find the area of the ring which is attached here. I have calculated the area but don't know whether my method is right or not

Answer 1

flat surface? one side perhaps?

Answer 2

Ok take r' and r as radius thats what i think

Answer 3

It's a flat surface

Answer 4

area with outer Radius - area with inner radius

Answer 5

pi [R^2 - r^2]

Answer 6

I did that but here dr is an infinitesimal radius

Answer 7

dr is the ghost of a departed value; so the area at dr is nothing

Answer 8

I got (2pi r)(dr) without considering the (dr)^2 part. Am I right here?

Answer 9

dr is is not a value perse; its a limit of a reimann sum i believe

Answer 10

i spose the "area" would amount to the circumference in some thought or another

Answer 11

But here dr is a thickness though

Answer 12

dr is not a thickness unless you are going to use it as some finite value; then the conventional thing is to describe it as \(\triangle\)r

Answer 13

O is the centre here with r the radius and dr the thickness, even I am in confusion here

Answer 14

as \(\lim_{\triangle r->0}=dr\)

Answer 15

but since the thickness is 0 when it equals "dr"; there is no area left to define

Answer 16

Yeap...........Thanks. I was solving some boring electric field problem here and came across with this one

Answer 17

:) youre welcome