Sector of a circle

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Concept #1 CIRCLE CENTRE
DEFINITION: The fixed point in the circle is called centre.

Learning objectives

 * 1) Define circle
 * 2) give examples for circles
 * 3) Locate centre for the given circle.

Notes for teachers
Define circle and centre with the help of a diagram

Activity No # 1 To locate centres for circles
20 minutes For the teacher: chalk piece, geometry set. for the student: paper Instructions for the teacher: Draw few circles of different radii and name the centres Instructions for the student : name the centres of different circles Identify the centre. Is there a circle with 3/4/5 centres?
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 * 1) How many centres does a circle has?
 * 2) Where does the centre of the circle lie? (inside/outside)
 * Question Corner

Activity No # 2

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Concept #2 Radius and Diameter
DEFINITION: RADIUS:A straight line drawn from centre to the circumference DIAMETER:A straight line drawn through the centre and terminated both ways by the circumference.

Learning objectives
to draw circle to draw a diamter use of geometrical instruments

Notes for teachers
explain the concepts using requisite diagrams. Conduct this activity.

Activity No #1
20 minutes different coloured circular cutouts instructions to the teacher: The teacher distributes the papeAre the students standing on the circumference of the circle considered to be in the interior or in the exterior ? Justify.r cut outs to all the students. Ask every student to make 2 equal parts by folding. What happens if it is folded again to get equal parts? Ask the students to identify the folded lines/marks
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 * 1) The student should have knowledge of circles.
 * 2) The student should have skill of paper folding
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instructions to the student: fold the paper cut out as per instructions observe and mark the folded line. Identity the diameter and radius. how many such radii and diameters can be drawn to a given circle?
 * Evaluation
 * 1) Was the student successful in marking radius and diamter?
 * 2) Was the student successful in folding and marking?
 * 3) Was the student able to relate radius and diameter.
 * Question Corner

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Concept #3 CIRCUMFERENCE
DEFINITION: The bounding line of the circle is called circumference

Learning objectives
The student needs to understand that the circumference is the outer boundary of a circle.

Notes for teachers
Explain that every point on the circumference is at equidistant from the centre.

Activity No #1
10 minutes. white paper, compass and colour pencils. The student should know to use the compass. The student should understand the circumference as outer boundary. Geogebra Instructions to the teachers Ask the children to draw circles. Instructions for the students Colour circumference by fitting small colour pencil in compass itself. Observe for the skill in using compass and drawing the circle. Is the distance between centre of the circle and its circumference constant ? What is the distance between the center of a circle and its circumference called?
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Learning objectives

 * The student should be able to understand that a diameter divides the circle into two equal halves and each such half is a semicircle or hemicircle.
 * The student learns how to form a semicircle by joining any two points on the circumference through its centre.

Notes for teachers
Show children the forming of semicircle by drawing diameter.

Activity No # 1
Bring cut circles of different sizes, fold them into exact halves and help them recognise semicircles. Let them colour each half with different colour.

Sub units of activities: This is a classroom individual activity. Materials: White paper, crayons. 15 minutes. White paper, crayons. The students should have prior knowledge of circle and diameter. Geogebra Instructions to the teacher: Ask children the previous day to cut circles of given radius and bring.
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Instructions to the students: Instruct them to fold circle into exact half. Draw diameter on folded line and colour each half with different colour. Were the students able to draw and cut perfect circles? Was the folded line (diameter) passing through the center of circle? In how many different ways can you draw semicircles for a given circle?
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Concept #5 Interior and Exterior of a circle
DEFINITION: INTERIOR:The set of all points of its plane whose distance from its centre is less than the length of its radius EXTERIOR:The set of all points of its plane whose distance from its centre is greater than the length of its radius

Learning objectives
The student needs to understand that any points on the planar surface of the circle within its circumference are said to be interior points and points on the outside of circumference are said to be its exterior points.

Notes for teachers
This knowledge is important to understand secant and tangent to the circle.

Activity No #1
'A game of tiger and goat.' Draw a circle on the playground. Make children stand on its circumference. Call one student inside the circle to be a goat and other student on the exterior would be the tiger. The tiger tries to get into the circle interior to catch the goat. All other students on the circumference defend the entry of tiger. If tiger forces itself inside, the goat is let out. If the tiger succeeds in catching the goat, the student enacting goat becomes out. Next two more students come forward to be the next goat and tiger and hence the game continues. Sub units of activity: This is an outdoor group activity Instructions to the teachers: Let this be a fun filled activity and during the game use the terms circle, circumference, interior and exterior. Instructions to the students: Identify who is in the interior of circle and who is in the exterior. 30mins A meter length wool nailed to ground (to be centre of circle) and tied to stick on the other side to help draw a perfect circle. The students need to know that the circumference of the circle is its boundary and understand the terms interior and exterior of the circle.
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Guage if the students have understood the meaning of the terms interior and exterior. Are the students standing on the circumference of the circle considered to be in the interior or in the exterior ? Justify.
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Activity No #
30 minutes A meter length wool nailed to ground (to be centre of circle) and tied to stick on the other side to help draw a perfect circle. The students need to know that the circumference of the circle is its boundary and understand the terms interior and exterior of the circle. Instructions to the teachers: Let this be a fun filled activity and during the game use the terms circle, circumference, interior and exterior. Instructions to the students: Identify who is in the interior of circle and who is in the exterior. Guage if the students have understood the meaning of the terms interior and exterior. Are the students standing on the circumference of the circle considered to be in the interior or in the exterior ? Justify.
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Concept #6 Chord
DEFINITION: line joining any two points on the circumference

Learning objectives

 * The students should understand that the chord is a line segment joining any two distinct points on the circle
 * The students should understand that the longest chord in any circle is its diameter.

Notes for teachers

 * Explain the concept by drawing chords of different sizes.
 * Make the students understand that the length of the chord increases as it moves closer to the centre and decreases as it moves away from the center.

Activity No # 1
Fold the cut-circular paper at different points. Draw folded lines with different coloured pencils and observe the length of chords. Circles cut from white paper, colour pencils, scale. The students should have the knowledge of circle, diameter, circumference and line segment. Instructions to the teacher: Instruct the children to get cut circles ready: Instructions to the children: Fold the circle at different points and try to form the smallest and biggest chords. Observe to see if the children are able to fold and mark the chord accurately. Name the chord that passes through the center of the circle. What happens to the length of the chord as it moves away from the centre?
 * Estimated Time :20 minutes.
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Learning objectives

 * The students should understand that an arc is a slice of a circle included between two radii of the circle.
 * The students should understand the two types of arcs -minor arc and major arc. The larger arc is called a major arc and the smaller one is called minor arc.

Notes for teachers
Explain the concept of arc by drawing a circle and two radii within it. The part of the circle enclosed within and outside the two radii are called its arcs.

Activity No # 1
Get a circular chapati. Cut out a slice by marking its radii and depict major and minor arcs. This is a classroom individual activity.

Chapatis, scissors and scale. The students should have prior knowledge of circle, circumference, radius and line segment. Instructions to the teacher: Instruct the children previous day to get circular chapatis. Instruct them to mark the center of circle by folding it twice over.
 * Estimated Time : 10 minutes
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Instructions to the students: Roll chapatis and cut using circular lids to get exact circle shape. Were the chapatis exact in circle shape. Could the students mark its centre, radii and identify the major and minor arcs. What is the longest arc of a circle which forms the circle called? Can you distinguish major and minor arcs when the two radii involved are at 180 degrees.
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