Surface Area of Sphere is the area occupied by the curved surface of the sphere. We know that, a sphere is a three-dimensional solid figure that is symmetrical in shape, with every point on its surface equidistant from its center.
Let’s learn the formulas of Surface Area of Sphere and how to use them with the help of solved examples.
What is Surface Area of Sphere?
The surface area of a sphere is the region covered by the outer surface in the 3-dimensional space. It can be said that a sphere is the 3-dimensional form of a circle. The surface area of a sphere formula is given in terms of pi (Ï€) and radius.
Formula Related to Surface Area of Sphere | |
---|---|
Surface Area of a Sphere | 4Ï€r^{2} |
Surface Area with Diameter | Ï€d^{2} |
Curved Surface Area of a Sphere | 4Ï€r^{2} |
Total Surface Area of a Sphere | 4Ï€r^{2} (Same as curved surface area) |
Surface Area of Sphere Formula
Formula for surface area of a sphere :
Surface Area of Sphere = 4Ï€r^{2}
Surface Area of Sphere Formula using diameter:
Surface Area of Sphere = Ï€d^{2}
where, r is the radius of the sphere.
Derivation of Surface Area of Sphere
We know that a sphere is round in shape, so to calculate its surface area, we can connect it to a curved shape, such as a cylinder. A cylinder is a three-dimensional figure that has a curved surface with two flat surfaces on either side.
Let’s consider that the radius of a sphere and the radius of a cylinder to be the same, so the sphere can perfectly fit into the cylinder.
Therefore, the height of the sphere = height of a cylinder = the diameter of a sphere.
Surface area of a sphere = Lateral surface area of a cylinder
We know that,
The lateral surface area of a cylinder = 2Ï€rh,Â
Where r is the radius of the cylinder and h is its height.
We have assumed that the sphere perfectly fits into the cylinder. So, the height of the cylinder is equal to the diameter of the sphere.
Height of the cylinder (h) = Diameter of the sphere (d) = 2r (where r is the radius)
Therefore,
The Surface area of a sphere = The Lateral surface area of a cylinder = 2Ï€rh
Surface area of the sphere = 2Ï€r Ã— (2r) = 4Ï€r^{2}
Hence,Â the surface area of the sphere = 4Ï€r^{2 }square units
How to Find Surface Area of Sphere?
The surface area of a sphere is simply the area occupied by its surface. Let’s consider an example to see how to use its formula.
Example: Find the surface area of a sphere of radius 7 cm.
Step 1: Note the radius of the given sphere. Here, the radius of the sphere is 47 cm.
Step 2: We know that the surface area of a sphere = 4Ï€r^{2}. So, substitute the value of the given radius in the equation = 4 Ã— (3.14) Ã— (7)^{2} = 616 cm^{2}.
Step 3: Hence, the surface area of the sphere is 616 square cm.
Curved Surface Area (CSA) of Sphere
The sphere has only one curved surface. Therefore, the curved surface area of the sphere is equal to the total surface area of the sphere, which is equal to the surface area of the sphere in general.
Therefore,
CSA of a Sphere = 4Ï€r^{2}
Total Surface Area (TSA) of Sphere
As the complete surface of the sphere is curved thus total Surface Area and Curved Surface Area are the same for the Sphere.
TSA of Sphere = CSA of Sphere
Related :
- Radius
- pi (Ï€)
- Surface Area of Cone
- Surface Area of Cuboid
- Surface Area of a Cube
- Volume of Sphere
- Surface Area Formulas
Surface Area of Sphere Examples
Let’s solve questions on the Surface Area of Sphere.
Example 1: Calculate the total surface area of a sphere with a radius of 15 cm. (Take Ï€ = 3.14)
Solution:
Given, the radius of the sphere = 15 cm
We know that the total surface area of a sphere = 4 Ï€ r^{2} square units
= 4 Ã— (3.14) Ã— (15)^{2}
= 2826 cm^{2}
Hence, the total surface area of the sphere is 2826 cm^{2}.
Example 2: Calculate the diameter of a sphere whose surface area is 616 square inches. (Take Ï€ = 22/7)
Solution:
Given, the curved surface area of the sphere = 616 sq. in
We know,
The total surface area of a sphere = 4 Ï€ r^{2} square units
â‡’ 4 Ï€ r^{2} = 616
â‡’ 4 Ã— (22/7) Ã— r^{2} = 616
â‡’ r^{2 }= (616 Ã— 7)/(4 Ã— 22) = 49
â‡’ r = âˆš49 = 7 in
We know, diameter = 2 Ã— radius = 2 Ã— 7 = 14 inches
Hence, the diameter of the sphere is 14 inches.
Example 3: Find the cost required to paint a ball that is in the shape of a sphere with a radius of 10 cm. The painting cost of the ball is â‚¨ 4 per square cm. (Take Ï€ = 3.14)
Solution:
Given, the radius of the ball = 10 cm
We know that,
The surface area of a sphere = 4 Ï€ r^{2 }square units
= 4 Ã— (3.14) Ã— (10)^{2}
= 1256 square cm
Hence, the total cost to paint the ball = 4 Ã— 1256 = â‚¨ 5024/-
Example 4: Find the surface area of a sphere whose diameter is 21 cm. (Take Ï€ = 22/7)
Solution:Â
Given, the diameter of a sphere is 21 cm
We know,
diameter = Â 2 Ã— radius
â‡’ 21 = 2 Ã— r â‡’ r = 10.5 cm
Now, the surface area of a sphere = 4 Ï€ r^{2} square units
= 4 Ã— (22/7) Ã— (10.5)Â
= 1386 sq. cm
Hence, the total surface area of the sphere = 1386 sq. cm.
Sphere Area Formula FAQs
What is Surface Area of Sphere?
The surface area of a sphere is given by the formula,Â
Surface area = 4Ï€r^{2}
Where r is the radius of the sphere.
What is Surface Area of Hemisphere?
The surface area of a hemisphere is given by the sum of half of the sphere’s surface area and the base area (which is circular), that is,
S.A. = 2Ï€r^{2 }+ Ï€r^{2}= 3Ï€r^{2}
Thus, the surface area of a hemisphere = 3Ï€r^{2}
What is Lateral Surface Area of Sphere?
The lateral surface area is equal to the surface area of the sphere, which is equal to the curved surface area of the sphere.
Why is Surface Area of Sphere 4 Times the Area of Circle?
Surface area of a sphere is four times the area of a circle because a sphere with radius, r can be thought of as composed of circles with the same radius. The formula for the surface area of a sphere, 4Ï€r^{2} is derived from the fact that its surface area is equivalent to the lateral surface area of a cylinder with the same radius and height equal to the diameter of the sphere. The diameter is twice the radius, thus leading to the factor of four.
How Does Surface Area of Sphere Change When Radius is Halved?
When the radius of a sphere is halved, its surface area becomes one-fourth of the original surface area. This is because the surface area formula, 4Ï€r^{2} , involves the square of the radius, so halving the radius squares one-fourth.
How does Surface Area of Sphere Change When Radius is Tripled?
When the radius of a sphere is tripled, its surface area increases by a factor of nine. This is because the surface area is proportional to the square of the radius (4Ï€r^{2} ) , so tripling the radius (3r) leads to 4Ï€(3r)^{2} = 9Ã—4Ï€r^{2} , which is nine times the original surface area.