1. Semicircle basics

2. Semicircle A semi-circle is half part of a circle
When a circle is divided by it diameter, the two equal parts are called semi-circles.
The blue shaded region in the image represents a semi-circle.
Semicircle

3. Perimeter of Semicircle
In a semi circle, the perimeter is made up of half the circumference (arc) of the circle and the diameter of the circle Perimeter = x (circumference of circle) + d = x (2πr) + d Perimeter = πr + d Perimeter = πr + 2r (∵ d = 2r ) Perimeter of semicircle = r(π + 2)

4. Area of a Semicircle
The area of a semicircle is half the total area of a circle. Area of semicircle = x (area of circle) ∴ Area of semicircle =
Area of semicircle

5. Perimeter of semi circle P = πr + 2r
Question 1 : The diameter of a semi circle is 28 cm. Calculate the perimeter and area of the semicircle. Solution: Given: d = 28cm So, we first find radius r = d/2 = 28/2 = 14 To find: perimeter and area of semicircle 28
Perimeter of semi circle
P = πr + 2r
= 22 X x 14 =
Perimeter = 72 cm
Area of semi circle
A =
= 22 x 14
Area = 308 cm 7 2

6. Perimeter of semi circle P = πr + 2r
Question 2: Find the perimeter and area of a semi circle whose radius is 7 cm. Solution: Given: r = 7cm To find: perimeter and area of semicircle
r=7
Perimeter of semi circle
P = πr + 2r
= x 7 =
Perimeter = 36 cm
Area of semi circle
A =
= 11 x 7
Area = 77 cm 11

7. Recap A semicircle is half part of a circle
Perimeter of a semicircle = r(π + 2)
Area of a semicircle =

8. Try these Find the perimeter of a semi circle whose radius is 21 cm.
Find the area of a semi circle whose diameter is 14 cm.