### Math - Class 4 – Circles Glossary/Circle Basics/ Radius, diameter, center, chord and circumference of a circle/Parts of a Circle - Key Points/Notes/Worksheets/Explanation/Lesson/Practice Questions

**Tags:**Radius, Radii, Diameter, Chord, Arc and Circumference of circle, Circle basics for grade 4, Free Worksheet PDF on Circle for fourth Grade, Parts of circle for 4rth standard, Identifying parts of circle, Lesson on Circle, Step to calculate radius and diameter of circle, How to calculate radius and diameter of circle for class IV, Relation between radius and diameter for class 4, Quiz on circle, What is a circle, Define circle, A circle is a closed curve. Points on the border of the circle are equidistant from the center of the circle. What is a radius, Define radius, Radius is any line segment from center to the edge of the circle. Define arc, What is a diameter, Line segment joining any two points on the edge of the circle is called chord. what is a line segment, what is a circumference, The length of the boundary of a circle is called circumference of a circle.### Circle

__Let’s do an activity to understand the basics of circle__**Step 1:**Trace a circle on a paper using any circular object such as a big bottle cap or a bangle and cut along the traced lines.**Step 2:**Fold the cut circle into half. We will get semicircle. Now unfold the semicircle and see the pleat formed is called the__diameter of circle__.**Step 3:**Again fold the half folded circle again into half. We will get a quadrant. Now open the fold of__quadrant__. We will see 4 pleat__meeting at a common point. This point is called center of the circle__and pleats meeting at a point are called radii of the circle.**Step 4:**If we fold any part of the circle now. The pleat formed is called the__chord of the circle__.**Step5:**The length of the boundary formed after tracing is called the__circumference of the circle__.#### Circle - A circle is a closed curve. Points on the border of the circle are equidistant from the center of the circle.

#### Radius – Radius is any line segment from center to the edge of the circle.

All radii of the circle are equidistant from the edge of the circle i.e. all radius are equal in length.

#### Diameter – Diameter is a line segment that starts at one side of circle, passes through the center of the circle and touches the other end of the circle.

Diameter = 2 x radius

Radius = D/2

__Example 1:__Radius = 6 cmDiameter = 2 x 6 cm

= 12 cm

__Example 2:__Diameter = 18 cmRadius = 18/2

= 9 cm

All diameter of the given circle are equal in length. Each diameter is formed of two radii. Diameter is twice the length of the radius.

#### Circumference - The length of the boundary of a circle is called circumference of a circle.

#### Chord – Line segment joining any two points on the edge of the circle is called chord. Diameter is longest chord of the circle.

#### Arc – Any part of the circumference of the circle is called arc.

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