13. If a circle and a sphere have same
radii, then the ratio between the area
of the circle to the surface area of
the sphere is *
O 1:4
O 4:1
O 1:1
none of these
Answers
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ANSWER
Since, the height of a sphere is the diameter, the cone and cylinder have height 2r.
Then
Curved surface area of Sphere=4πr²
Curved surface area of cylinder =2πr(2r)=4πr²
Curved surface area of cone = πrl
where, l=
(r
2
+h
2
)=
(r2+(2r)
2
)=
5r
2
=r
5
⇒ Curved surface area of cone =π
5r
2
Now,
ratio of CSA 's a sphere ,cylinder and a cone = 4πr
2
:2πrh:πrl
=4πr
2
:4πr
2
:πr
2
5
=4:4:
5
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