# Identification of Circle/Radius / Diameter

## Students` Learning Outcomes

• Identify circle, its radius and diameter.

• Calculate perimeters of squares, rectangles and triangles.

## Information for Teachers

• The diameter is the line segment that goes through the center of the circle and has end points at the edge of the circle.
• Diameter is the largest distance between any two points on the circle. AD, BE and FC are diameters in the given circle.

• Radius is the half of diameter. It is the distance of the center of the circle from any point on the boundary of the circle. GC, GD, GF etc. are the radii of circle (radii is the plural of radius).

• The sum the lengths of al sides of a simple figure called perimeter.
• While teaching the lesson, also consult textbook where and when applicable.

### Material / Resources

Writing board, chalk/marker, duster, glass, sheets of paper, pencil, ruler, scissors, some circular shape objects (drinking glass, cap of water bottle, inkpot, etc.), textbook

### Introduction

Activity 1

• Ask 8 to 10 students to stand in front of class and to join their hands so that they can make a circular shape. Ask them to sit down.

• Ask the other students, what shape they can see. After taking their response tell them that the students are showing the shape of a circular.

Activity 2

• Select a student from the class and ask him/ her to draw a circle with the help of a glass.

• Guide him / her in placing the drinking glass with its open end on a flat sheet of a paper.
• Trace around the opening of the drinking glass with a pencil.
• Remove the glass from the paper, what is this shape?
• Cut the circle with the help of scissors. Show this cutout of circle to other students.
• Let`s identify its diameter and radius.

### Development

Activity 1

• Divide the class into 3 or 4 groups. Give sheets of paper and any circular object (drinking glass, cap of water bottle, inkpot, etc.) to students.

• Ask the students to draw the circle and make the cutout of circle.

Activity 2

• Ask the students: what is a semicircle. After taking their response, demonstrate to the students that we will get the semicircle by folding the circle into two equal halves.
• Ask the students to fold their circles to make two semicircles. And then unfold the circle. They will see a crease on the circle.

• Ask the students to draw a line segment following this crease. Tell them that this line segment goes through the center of the circle and has end points at the edge of the circle. Explain to them that this line segment is called diameter of circle.

• As the students to draw another line segment to show the diameter of the circle. Write its name and measure its length also.

Activity 3

• Ask the students: what is quarter circle? After taking their response, demonstrate that how we will get the quarter-circles by folding the semicircles into two equal halves.

• Ask the students to fold their semicircles to make four quarter-circles.
• Unfold the circle.
• You will see two line segments on the circle which are cutting each other at point C. this point is called Centre of the circle.
• Ask the students to draw a line segment that starts from the center of the circle and has ends at the edge of the circle.
• Tell the students that this is called the radius of the circle.

• Ask the students to draw another line segment to show the radius of the circle and also write its name and measure its length also.

Activity 4

• Demonstrate the concept of perimeter on the board.

• Ask: How can we find out the total length of all sides of this triangle?
• Sum of lengths of all sides = 5cm + 5cm + 7cm = 17cm.
• What is the total length of all sides of this shape called?
• Tell the students that the sum of lengths of all sides of this figure is called perimeter.
• What is the perimeter of this triangle? (17cm)
• Thus perimeter of the above figure is 17cm.
• Ask the students to find the perimeters of the following shapes.

• Perimeter = 7 cm+ 7cm + 7cm + 7cm = 28cm
• Observe their work and guide the slow learners.

### Sum up / Conclusion

• Repeat the main points from the lesson.
• Diameter is the line segment that goes through the center of the circle and has end points at the edge of the circle.

• The length of the line segment that starts from the center of the circle and bends at the edge of a circle is called radius of the circle.

• The sum of the lengths of all sides of a figure is called perimeter.

### Assessment

• Name the line segment that shows the diameter of the circle given below.
• Name the line segments that shows radius of the circle given below.