Circles calculate area circumference radius and diameter :
Here we are going to see some example problems to understand how to calculate area and circumference of circle.
The radius is a line segment with one end point at the centre and the other end on the circle. It is denoted by ‘r’.
Diameter is a chord passing through the centre of the circle. It is denoted by ‘d’.
The diameter is the longest chord. It is twice the radius.(i.e. d = 2r )
Circumference of a circle:
Can we find the distance covered by an athlete if he takes two rounds on a circular track. Since it is a circular track, we cannot use the ruler to find out the distance.
The distance around a circle is called the circumference of the circle, which is denoted by ‘C’. i.e., The perimeter of a circle is known as its circumference.
Circumference of circle = 2 π r
Area of circle :
The area of a circle is the number of square units inside that circle
Area of circle = π r²
Example 1 :
Find out the circumference of a circle whose diameter is 21 cm.
Diameter = 21 cm
Radius = 21/2 = 10.5 cm
Circumference of circle = 2 π r
= 2 (22/7) x 10.5
= 44 x 1.5
= 66 cm
Hence the circumference of circle is 66 cm.
Example 2 :
A wire of length 88 cm is bent as a circle. What is the radius of the circle.
Length of the wire = circumference of the circle
2 π r = 88 cm
2 x (22/7) x r = 88
r = (88 x 7)/(2 x 22)
r = 14 cm
Hence the radius of the circle is 14 cm
Example 3 :
The diameter of a bicycle wheel is 63 cm. How much distance will it cover in 20 revolutions?
When a wheel makes one complete revolutions,
Distance covered in one rotation = Circumference of wheel
Circumference of the wheel = 2πr units
= 2 x (22/7) x (63/2) cm
= 22 x 9 = 198 cm
For one revolution, the distance covered = 198 cm
For 20 revolutions, the distance covered = 20 × 198 cm
= 3960 cm
= 39 m 60 cm [100 cm = 1 m]
Hence the distance covered in 20 revolution is 39 m 60 cm
Example 4 :
A scooter wheel makes 50 revolutions to cover a distance of 8800 cm. Find the radius of the wheel.
= Number of revolutions/Circumference
2πr = 8800/50
2πr = 176
2 x (22/7) x r = 176
r = 176 x (7/22) x (1/2)
r = 28 cm
Hence the radius of the wheel is 28 cm
Example 5 :
The radius of a cart wheel is 70 cm. How many revolution does it make in travelling a distance of 132 m.
Given: r = 70 cm, Distance travelled = 132 m.
Circumference of a cart wheel = 2πr
= 2 x (22/7) x 70
= 440 cm
= Number of revolutions x Circumference
Number of revolutions
= Distance travelled/Circumference
= 132 m/440 cm
Hence the number of revolution is 30.
After having gone through the stuff given above, we hope that the students would have understood "Circles calculate area circumference radius and diameter".
Apart from the stuff given above, if you want to know more about "Circles calculate area circumference radius and diameter", please click here
Apart from the stuff given in this section, if you need any other stuff in math, please use our google custom search here.
APTITUDE TESTS ONLINE
ACT MATH ONLINE TEST
TRANSFORMATIONS OF FUNCTIONS
ORDER OF OPERATIONS
Decimal place value worksheets
Area and perimeter
Different forms equations of straight lines
MATH FOR KIDS
HCF and LCM word problems
Word problems on quadratic equations
Word problems on comparing rates
Ratio and proportion word problems
Converting repeating decimals in to fractions