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SAI International School
                                                      CLASS-VII

               Mathematics
               CHAPTER-11: Area and Perimeter
               LESSON NOTES-5


               SUBTOPIC: Circumference of Circle


               Introduction:A circle is a simple closed shape where all points have the same
               distance from the centre.
                     We have seen many shapes such as wheel, dining plate, coin etc. All these
                       shapes are in the form of circle.
                     The center of a circle is the center point in a circle, from which all the
                       distances to the points on the circle are equal.
                     The radius is the distance from the center to any point on the circle.
                     Diameter of the circle is defined as the distance across the circle.
                     The length of any chord passing through the center is called the diameter of
                       the circle. It is twice the radius. i.e. diameter = 2 x radius (d = 2r)
                   



















                                                     In the given figure O is the centre, OP is the
                       radius and PQ is the diameter of the circle.

               Circumference of the Circle:The distance around the outside of the circle is
               called the circumference of the circle.
                     Let r be the radius of the circle.

                     Now, circumference of the circle(C)= πd= π × 2r    or      C = 2πr.
                       (Where C is the circumference, r is the radius and d is the diameter of the
                       circle)
                                                              22
                     The value of π (pi) is approximately      or 3.14.
                                                              7
                     Hence the circumference of the semicircle will be half the circumference of the
                                 2    
                       circle i.e.     = πr
                                  2
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