Sub. :- Mathematics Circle Std. :- 6 th Chapter no. 26

Definition: A circle can be defined as the curve traced out by a point that moves so that its distance from a given point is constant. The word "circle" derives from the Greek, kirkos "a circle," from the base ker- which means to turn or bend. The origins of the words "circus" and "circuit" are closely related.circuscircuit

Definitions Related to Circles

origin: the center of the circle Chord: a line segment within a circle that touches 2 points on the circle. Diameter: the longest chord, a line segment whose endpoints lie on the circle and which passes through the centre; or the length of such a segment, which is the largest distance between any two points on the circle.endpoints Radius: a line segment joining the center of the circle to any point on the circle itself; or the length of such a segment, which is half a diameter. Tangent of circle: a straight line that touches the circle at a single point. Secant : an extended chord, a straight line cutting the circle at two points. Circumference: the distance around the circle. pi ( π ): A number, , equal to (the circumference) / (the diameter) of any circle. π

B CD A o P Q R S Fig 2 Name all radii and diameters shown in Fig 2

Draw the circles of the radii given below, using compass. 1) 2.5 cm 2) 3.5 cm 3) 2 cm 4) 3 cm

Diameter = 2 x radius of circle The radii of some circles are given below.What are their diameters ? Exercise :- 1) 8cm 2) 3.5 cm 3) 2 cm 4) 1.6 cm

Answers :- Diameter = 2 x radius of circle = 2 x 8 = 16 cm 1)Here Radius = 8 cm

Draw a circle of any radius. Now draw three or five radii in this circle. Using divider measure their lengths. Again draw three or five diameters in this circle. Using divider measure their lengths. Activity 1 Write your conclustion

1) All radii of a circle are equal in length. 2) All diameters of a circle are equal in length. Properties of the radius and diameter.

Draw a circle of any radii Draw someradii in this circle. Again draw some diameters in this circle. Activity 2 How many radii & diameters we can draw in this circle ? Answer is innumetable …………

Arc of a circle In adjacent fig. of the circle A & B are two points on the circle, which divides the circle in two parts. Each part is called an arc.

Here, two arcs are formed. arc ACB & arc AB.

Write the names of the arcs in the following Fig.

The interior and the exterior of the circle

Complete the following table Fig. Name of the points in the interior Name of the points in the exterior Name of the points on the circle 1 2 Fig. 1 Fig. 2