Areas Related to Circles Formulas CBSE Class 10 Maths

Circumference of a Circle or Perimeter of a Circle

The distance around the circle or the length of a circle is called its circumference or perimeter.
Circumference (perimeter) of a circle = πd or 2πr,
where d is a diameter and r is a radius of the circle and π = $\frac { 22 }{ 7 }$
Area of a circle = πr²
Area of a semicircle = $\frac { 1 }{ 2 }$ πr²
Area of quadrant = $\frac { 1 }{ 4 }$ πr²

Perimeter of a semicircle:
Perimeter of a semicircle or protractor = πr + 2r

Area of the ring Formulas :
Area of the ring or an annulus = πR² – πr²
= π(R² – r²)
= π (R + r) (R – r)

Length of the arc AB = $\frac { 2\pi r\theta }{ { 360 }^{ 0 } }$ = $\frac { \pi r\theta }{ { 180 }^{ 0 } }$

Area of sector formula:

Perimeter of a sector Formula:

Perimeter of sector OACBO = Length of arc AB + 2r
= $\frac { \pi r\theta }{ { 180 }^{ 0 } }$ + 2r

Other important formulae:

Distance moved by a wheel in 1 revolution = Circumference of the wheel.
Number of revolutions in one minute = $\frac { Distance moved in 1 minute }{ Circumference }$
Angle described by minute hand in 60 minutes = 360°
Angle described by hour hand in 12 hours = 360°
The mid-point of the hypotenuse of a right triangle is equidistant from the vertices of the triangle.
The angle subtended at the circumference by a diameter is always a right angle.

Area of a segment Formula Class 10 :

Area of minor segment ACBA = Area of sector OACBO – Area of ΔOAB
= $\frac { \pi { r }^{ 2 }\theta }{ { 360 }^{ 0 } } -\frac { 1 }{ 2 } { r }^{ 2 }sin\theta$
Area of major segment BDAB = Area of the circle – Area of minor segment АСВА
= πr² – Area of minor segment ACBA.
If a chord subtends a right angle at the centre, then
Area of the corresponding segment = $\left( \frac { \pi }{ 4 } -\frac { 1 }{ 2 } \right) { r }^{ 2 }$
If a chord subtends an angle of 60° at the centre, then
Area of the corresponding segment = $\left( \frac { \pi }{ 3 } -\frac { \surd 3 }{ 2 } \right) { r }^{ 2 }$
If a chord subtends an angle of 120° at the centre, then
Area of the corresponding segment = $\left( \frac { \pi }{ 3 } -\frac { \surd 3 }{ 4 } \right) { r }^{ 2 }$