In this video you will learn Areas related to circles - perimeter and area of a circle
To watch more such videos -
Visit - www.letstute.com
YouTube - www.youtube.com/letstute
Thank you
Areas related to circles - perimeter and area of a circle for class 10 maths.
1. Areas Related To Circles
Problems based on
Perimeter and area of a circle
Chapter : Areas Related To Circles Website: www.letstute.com
2. Problems based on
Perimeter and area of a circle
Q) Find the circumference and area of the circle of radius
7.2cm.
Given: Radius of the circle = 7.2cm
To Find: a) Circumference of the circle = ?
b) Area of the circle = ? O
7.2 cm
Chapter : Areas Related To Circles Website: www.letstute.com
3. Problems based on
Perimeter and area of a circle
Solution: Let the radius of the circle be ‘r’
r=7.2cm ---------- (given)
a) Circumference = 2πr
=2x22x7.2cm
7
= 45.26 cm
b) Area = πr2
= 22x7.2x7.2cm2
7
= 162.93 cm2
O
7.2 cm
Chapter : Areas Related To Circles Website: www.letstute.com
4. Problems based on
Perimeter and area of a circle
Result: a) Circumference= 45.26cm
b) Area= 162.93cm2
Hence, the circumference of the circle is
and its area is
45.26cm
162.93 cm2
O
7.2 cm
Chapter : Areas Related To Circles Website: www.letstute.com
5. Problems based on
Perimeter and area of a circle
Q) The diameter of a watermelon slice is 8cm. Find its
perimeter.
Given: Diameter = 8cm
To Find: Perimeter of the slice = ?
8cm
Chapter : Areas Related To Circles Website: www.letstute.com
6. Problems based on
Perimeter and area of a circle
Solution: Let ‘r’ be the radius of the watermelon slice.
8cm
r = Diameter = 8cm = 4cm
2 2
Perimeter = 1x 2πr+2r
of the slice 2
22
1
4 2 4
2
2
=20.57 cm
7
20.57cm
Result: Perimeter of the slice = 20.57 cm
Hence, the perimeter of the watermelon slice is
Chapter : Areas Related To Circles Website: www.letstute.com
7. Problems based on
Perimeter and area of a circle
Q) The difference between the circumference and diameter of a
wheel is 18cm. Find the radius of the wheel.
Given: Circumference - diameter=18cm
To Find: Radius of the wheel = ?
O
? cm
Chapter : Areas Related To Circles Website: www.letstute.com
8. Problems based on
Perimeter and area of a circle
Solution: Let the radius of the wheel be ‘r’
Circumference-Diameter = 18cm ------- (Given)
2πr-2r = 18cm
2r(π-1) = 18cm
2r
1
= 18cm
2r
= 18cm
2r x 15 = 18cm
22 7
7
7
r = 18x7 cm
2x15
22
7
O
? cm
Chapter : Areas Related To Circles Website: www.letstute.com
9. Perimeter and area of a circle
= 9x7 cm
15
= 3x7 cm
5
= 21 cm
5
= 4.2cm
Problems based on
Result: Radius of the wheel= 4.2cm
Hence, the radius of the wheel is 4.2cm
O
? cm
Chapter : Areas Related To Circles Website: www.letstute.com
10. Problems based on
Perimeter and area of a circle
Q) A wire is in the form of a circle of radius 50cm. It is bent
into a square. Determine the side of the square.
O
Before
Given : Radius of the circle = 50 cm
To Find: Side of the square = ?
Chapter : Areas Related To Circles Website: www.letstute.com
11. Problems based on
Perimeter and area of a circle
Solution: Let the radius of the circle be ‘r’
r = 50cm ---------- (given)
Length of the wire = Circumference of the circle
= 2πr
= 2x22x50cm
7
= 2200 cm
7
= 314.28cm
O
Before
Chapter : Areas Related To Circles Website: www.letstute.com
12. Problems based on
Perimeter and area of a circle
Let ‘x’ be the side of the square.
Perimeter of the square = Length of the wire (circumference)
4x = 314.28
x = 314.28
4
x = 78.57 cm
X cm
After
Hence, the side of the square is
78.57cm
Chapter : Areas Related To Circles Website: www.letstute.com
13. Visit us on – www.letstute.com
Subscribe us on www.youtube.com/letstute
Thank you
Editor's Notes
A very good day to all of you’ll out there…… before we move on to the first question, lets put on our thinking caps as we tackle some problems.
Moving on to the first question,
Find the circumference and area of the circle of radius 7.2cm.
We have been given that the radius of the circle is 7.2 cm.
We need to find 2 things, a) Circumference of the circle
b) Radius of the circle
So, ;let us see the solution…..
Firstly let us represent the radius of the circle to be r
R as we know is 7.2 cm
In order to find the circum., we need to use a formula. So, do you’ll remember the formula for circumference???
The formula is = 2πr
No by substituting the value of pie by 22/7 and r by 7.2, we get
=2x22x7.2cm
7
On firther simplifying this step, we get the answer to be 45.26 cm
= 45.26 cm
Cuming on to the b part,
We are asked to find out the area of the circle,
Area is given by the formula = πr2
By substituting pie by 22/7 and r by 7.2, we get
= 22x7.2x7.2cm2
7
On further simplificatn we get,
= 162.93 cm2
So, the result is a) a) Circumference= 45.26cm
b) Area= 162.93cm2
Hence, the circumference of the circle is 45.26cm
and its area is 162.93cm2
Let us see the next question, The diameter of a watermelon slice is 8cm. Find its perimeter.
Let us see what is given to us,
We have Diameter which is 8 cm
What we need to find is the perimeter of the slice.
Moving on to the solution, Lets us denote radius of the watermelon slice as r
We have been given diameter of the slice which is 8 cm. In order to find the radius, we have a formula.
Radius = diameter = 8 = 4
2 2
What we now need to find out is the perimeter of the slice.
The perimeter can be determibned by the formula 1x 2πr+2r
2
By substituting pie by 22/7 and r by 4, we get
½ x 2 x 22/7 x 4 + 2 x 4
By cancelling out 2, and further simplificatn, we gt,
The answer to b 20.57 cm
Thus, Hence, the perimeter of the watermelon slice is 20.57 cm
Let us now tackle the next questn which says that The difference between the circumference and diameter of a wheel is 18cm. Find the radius of the circle.
Firstly, let us see what is given to us.
We hve, Circumference - diameter=18cm
What we need to find is the radius.
Solution = Let r be the radius of the circle.
We have been given Circumference-Diameter = 18cm ------- (Given)
We already know the formula for the circumference of the circle. And that of diameter which is 2r
By using the respective formulas, we get,
2πr-2r = 18cm
By taking 2r common, we get
2r(π-1) = 18cm, now by substituting pie by 22/7, we get,
2r( 22/7 -1) = 18cm
On cross multiplication, we get,
2r(22-7 /7) = 18cm
On subtracting, 22 by 7, we get 15, thus the next step will be
2r x 15 = 18cm
7
As we need to determine the radius of the wheel, we need to isolate r by taking all d values on the RHS, so we get,
r = 18x7 cm
2x15
On further simplificatn, we get,
, Thus, the result is the radius of the circle is 4.2 cm
The next questn is A wire is in the form of a circle of radius 50cm. It is bent into a square. Determine the side of the square.
Lets see what is given to us, we have the radius of the circle which is 50 cm.
The circle is then bent into a sqaure.
What we need to determine is the side of the square after it has been bent.
Let us take a look at the solution,
Firstly, let us represent the radius of the circle as r,
Thus, r = 50 cm which is given to us.
We all know that the length of the square is equal to the circumference of the circle.
The circumference of the circle is given by the formula, 2πr
by substituting pie by 22/7 and r by 50, we get
= 2x22x50cm
7
By multiplyin 2x22x50, we get,
=2200
7
On further division, we get
= 314.28cm
Now, the wire which is in the form of a circle is bent into a square,
So, let us consider the side of the square to b ‘x’
Now, the Perimeter of the square = Length of the wire which is the (circumference)
The perimeter of the square is given by the formula 4x and we already found out the cicumference , thus we get,
4x = 314.28
as we need to find out the value of x, we need to isolate it by taking 4 to the RHS, thus we get, x = 314.28
4
On division, we get
x = 78.57 cm
Thus, the side of the square is 78.57 cm