Notes on Circles | Grade 7 > Compulsory Maths > Geometry: Triangles, Quadrilaterals and Circles | KULLABS.COM

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#### Circle and its different parts

A circle is a plane figure bounded by a curved line and every point of the line is equidistance from a fixed point called the centre of the circle.

1. Circumference of circle
The curved boundary line of a circle sis called its circumstance. The length of the circumference represents the perimeter of the circle.
The straight line is drawn from the centre of a circle to a point on its circumference is called the radius of the circle.
In the given figure, OA is the radius.
3. Chord of a circle
The straight line segment that joins any two points on the circumference of a circle is called the chords of a circle.
In the given figure, AB is the chord of the circle.
4. Diameter of a circle
The chord that passes through the centre of a circle is called the diameter of the circle. Diameter is also called the largest chord of any circle. In the given figure, CD is the diameter of a circle. The length of the diameter of a circle is two times its radius.
$$\therefore$$ Diameter = 2 × radius
5. Sector of a circle
The region inside a circle bounded by its two radii (plural of radius is radii) is called sector.
In the figure, the shaded region AOB is the sector.
6. Arc of a circle
The part of a curve between two given points on the curve of a circle is called an arc.
In the figure, AB is the arc.
7. Segment of a circle
The region bounded by an arc and its corresponding chord is called the segment of a circle.
In the given figure, the shaded region represents a segment.
8. Semi-circle
Half part of a circle is called a semi-circle. A diameter divides a circle into two halves and each half is the semi-circle.
In the given figure, ABC is a semi-circle.

• The length of the circumference represents the perimeter of the circle.
• The length of the diameter of a circle is two times its radius.
• Half part of a circle is called a semi-circle.
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### Very Short Questions

Solution:

Figure a) = radii OA and OB, sector OAXB and arc AXB

Figure b) = segment CDY and Chord CD

Figure c) = semi-circle MYN and MXN, diameter MN

Solution:

 Angle Opposite Arc $$\angle$$ABC AXC $$\angle$$PQR PYR $$\angle$$KLM, $$\angle$$KNM, $$\angle$$LKN, $$\angle$$LMN KPM, LN $$\angle$$ABC, $$\angle$$ADC, $$\angle$$BAD, $$\angle$$BCD AEC, BD

Solution:

Centre and Radii of figure a) = OA and OB

Centre and Radii of figure  b) = CP and DP

Centre and Radii of figure c) = EQ and FQ

Centre and Radii of figure d) = KM and KN

 Angle Opposite Arc $$\angle$$AOB AXB $$\angle$$CPD CYD $$\angle$$EQF EZF $$\angle$$MKN MSN

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• ### The straight line is drawn from the centre of a circle to a point on its circumference is called ______ .

the diameter of a square
the diameter of a circle

circle
circumstance
center

circumstance
diameter
semi-circle

an arc
the side