# Basic elements of a circle

From Karnataka Open Educational Resources

Investigation to understand basic parameters associated with circles.

### Objectives

To recognize different terms related to circles

### Estimated Time

40 minutes

### Prerequisites/Instructions, prior preparations, if any

Prior knowledge of point, lines, angles, polygons

### Materials/ Resources needed

- Digital : Computer, geogebra application, projector.
- Non digital : Worksheet and pencil, compass, strings
- Geogebra files : Elements of circles.ggb

Download this geogebra file from this link.

### Process (How to do the activity)

**Use geogebra file:**

- Connect a point on the circle and the center of the circle. Rotate to show line segment measures the same – establish radius
- Extend the radius from center of the circle to meet the circle.
- What is the measure of the line segment connecting the two points on the circle?
- Establish concept of diameter
- What is the difference between the radius and diameter?
- How are they related?
- What will happen if any two points on a circle are joined.

- Placing a point on the circle, can I measure the length along of the circle starting from this point to ending at the same point.
- Measure the circumference using distance tool.
- Will the circumference change if radius is changed. How are circumference and radius related.

**Hands on activity**

- Draw a circle with a compass, mark 5 points on the circle. Join the these points to the center of the circle. Take a thread and measure the segment length. Record the data in the table.

Circle No | Point 1 (Segment length from center) | Point 2 | Point 3 | Point 4 | Point 5 | Line drawn through center touching circle - length | Thread length |

Circle 1 | |||||||

Circle 2 | |||||||

Circle 3 |

For the circles drawn above measure the circumference using the thread to note the values. Also note your observations

Circle No | Point 1 (Segment length from center) | Point 2 | Point 3 | Point 4 | Point 5 | Length of line drawn through center touching circle | Circumference | Observation |

Circle 1 | ||||||||

Circle 2 | ||||||||

Circle 3 |

Draw a circle. Draw a line from any point on the circle passing through the center of the circle to intersect at another point on the circle. Mark the segment. Repeat the same taking different points on the circle. Note your observations

Segment through center | Length | Your observations |

Segment 1 | ||

Segment 2 | ||

Segment 3 |