Hemisphere
A hemisphere, in general, refers to half of the earth such as the northern hemisphere or the southern hemisphere. But in geometry, a hemisphere is referred to as a 3D figure made from cutting a sphere into two equal halves with one flat side. In real life we come across various objects that are in the shape of a hemisphere, for example, if we cut a cherry into half, we get a hemisphere-shaped cherry or if we cut a grapefruit into half we get a hemisphere. Let us learn more about a hemisphere, its properties and formulas in this article.
Definition of a Hemisphere
The word hemisphere can be split into hemi and sphere, where hemi means half and sphere is the 3D shape in math. Hence, a hemisphere is a 3D geometric shape that is half of a sphere with one side flat and the other side as a circular bowl. It is formed when a sphere is cut at the exact center along its diameter leaving behind two equal hemispheres. The flat side of the hemisphere is known as the base or the face of the hemisphere. Therefore, it is considered as an exact half of a sphere.
Properties of a Hemisphere
Since a hemisphere is the exact half of a sphere, they share very similar properties as well. They are as follows:
- A hemisphere has a curved surface area.
- Just like a sphere, there are no edges and no vertices in a hemisphere.
- It is not a polyhedron since polyhedrons are made up of polygons, but a hemisphere has one circular base and one curved surface.
- The diameter of a hemisphere is a line segment that passes through the center and touches the two opposite points on the base of the hemisphere.
- The radius of a hemisphere is a line segment from the center to a point on the curved surface of the hemisphere.
Difference Between Hemisphere and Sphere
We already know that a hemisphere is obtained from a sphere and the two objects share very similar properties, but there are a few differences as well. Listed below are the few differences between a sphere and a hemisphere.
| Hemisphere | Sphere |
|---|---|
| It is a 3D figure obtained by cutting a sphere in half. |
This is a 3D round figure used in geometry that has no edges and no vertices. |
| It has one flat side and one curved side. | This has no flat side and is only curved. |
| The volume of a hemisphere = (2/3)πr3 cubic units | The volume of a sphere = (4/3)πr3 cubic units |
|
Hemisphere has two surface areas, i.e., total surface area, and lateral surface area. The total surface area of hemisphere = 3πr2 and the lateral surface area of hemisphere = 2πr2. |
The surface area of sphere = 4πr2 |
Volume of a Hemisphere
The volume of a hemisphere is the total capacity of the hemisphere and it is the number of unit cubes covered inside that space. The volume of a hemisphere is measured in cubic units and is expressed as m3, cm3, in3, etc. Therefore, the formula to find the volume is:
Volume of Hemisphere = (2πr3)/3
Where π is the constant which is equal to 3.142 or 22/7, and r is the radius of the hemisphere. For a detailed explanation, you can check out this article on Volume of Hemisphere.
Surface Area of a Hemisphere
The surface area of a hemisphere can be calculated by the area of its circular base along with its curved surface. The hemisphere can either be hollow or a solid, according to that the surface area can be calculated. It is measured in square units and the formula is:
Surface Area of Hemisphere = 3πr2
Where π is the constant which is taken as 3.142 or 22/7, and r is the radius of the hemisphere. For a detailed study, you can check out this article on Surface Area of a Hemisphere.
Curved Surface Area of a Hemisphere
The curved surface of a hemisphere is considered the lateral area of a hemisphere. If the radius is given, we can find out the lateral surface area using the formula and it is measured in square units. The formula for finding the lateral surface area or the CSA of a hemisphere is:
Curved Surface Area of a Hemisphere = 2πr2
Where π is the constant taken as 3.142 or 22/7, and r is the radius of the hemisphere. A detailed explanation on this topic can be found in this article on Curved Surface Area of a Hemisphere.
☛ Related Articles
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Hemisphere Examples
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Example 1: Which of these is a hemisphere: a, b, c, or d?
Solution: We know that a hemisphere is a 3D figure that is half of a sphere. In the given figures, figure (c) is a hemisphere because it has one curved side and one flat side. Figure (a) is a triangle, figure (b) is a semicircle, and figure (d) is a cylinder.
FAQs on Hemisphere
What is a Hemisphere Shape in Math?
A hemisphere is a 3D figure which is obtained by cutting a sphere into two equal halves through its diameter. It has one curved side and one flat side called the face of the hemisphere or the great circle of the sphere which helps in forming the hemisphere. Some of the real-life examples of a hemisphere are a bowl, igloo, the top part of a mushroom, and so on.
What is the Formula to Find the Volume of a Hemisphere?
The volume of a hemisphere is expressed in cubic units and the formula which is used for the volume of a hemisphere is, Volume of Hemisphere = (2πr3)/3, where π is the constant measuring 3.142 or 22/7, and r is the radius.
What is the Formula to Find the Surface Area of a Hemisphere?
The surface area of a hemisphere is the curved part of the hemisphere and we calculate it by using this formula, Surface Area of Hemisphere = 3πr2, where π which is taken as 3.142 or 22/7, and r is the radius of the hemisphere. It should be noted that this is the total surface area of the hemisphere which includes the area of the base too.
What is the Formula to Find the CSA Area of a Hemisphere?
If the radius of a hemisphere is given, we can calculate the curved surface area (CSA) of a hemisphere by using this formula, Curved surface Area of a Hemisphere = 2πr2, where π is taken as 3.142 or 22/7, and r is the radius of the hemisphere. The lateral surface area is the area of the curved part of the hemisphere only. It does not include the area of the base which is in the shape of a circle.
Are Sphere and Hemisphere the Same?
The sphere and hemisphere are very similar in properties since the hemisphere is made from a sphere. When a sphere is cut into two equal halves, these two halves are called hemispheres. But one of the main differences between a sphere and a hemisphere is that a sphere does not have base but only a curved surface whereas a hemisphere has a base and one curved surface.
What is a Hollow Hemisphere?
If the space inside a hemisphere is hollow, it is known as a hollow hemisphere. A hollow hemisphere has two radii - an internal radius, for the inner circle (hollow region), and an external radius for the outside circle.
What is the Formula for the Base Area of a Hemisphere?
In a hemisphere, if its radius (r) is given, then its base area is given as Base Area of a Hemisphere = Area of the base circle = πr2 square units.
What does a Hemisphere Look Like?
A hemisphere looks like a cherry when cut into half. It also resembles the shape of an igloo.
How many Faces does a Hemisphere Have?
A hemisphere has one curved surface and one flat face in the shape of a circle. It is different from a sphere which has just one curved surface.