Circles
| Philosophy of Mathematics |
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Concept Map
Introduction
The following is a background literature for teachers. It summarises the things to be known to a teacher to teach this topic more effectively . This literature is meant to be a ready reference for the teacher to develop the concepts, inculcate necessary skills, and impart knowledge in Geometry - Circles from Class 6 to Class 10.
The first step is to understand how to define circles and related terms using geometric vocabulary. The next step is to understand what is Pi. That it is a constant and that for any circle the ratio of the circumference by the diameter is always a constant value Pi. The interesting properties of Pi – an irrational number can also be discussed here in the basic form. Ability for the child to do simple area and perimeter calculations. Next the learner should understand that the circle is a 2 dimensional plane figure and how to visualise solid 3-dimensional figures. What are the solid shapes that have a circle as a part of them. Mensuration – more complex area measurements which include circular shapes. Surface Area and Volume measurement of sold shapes such as cylinder, sphere and cone. Understand the properties of the circles by proving theorems deductively. Also acquire the skills of deductive proofs, understand that all the properties can be deduced from the axioms. Understand the relationship between lines and circles – secant and tangent
Additional Resources[edit | edit source]
OER[edit | edit source]
- Web resources :
- Cool math For clear and easy definitions.
- Wikipedia Has good explanations on circles.
- Khan academy Has good educative videos.
- Arvind gupta toys Contains good information.
- Books and journals
- School Geometry By Hall and Stevens. Part3 pageno 143. Contains basic definitions and proofs given by Euclid.
- Textbooks:
- Class 9 Mathematics contain simple description and theorems on circle
- CLASS 10
- Syllabus documents
Non-OER[edit | edit source]
- Web resources
- maths is funHere you get description of terms of circles
- Intersting facts this web link is full of circle facts.
- sparknotes Gives some more details about properties of circles
- www.regentsprep.com conatins good objective problems on chords and secants
- www.mathwarehouse.com contains good content on circles for different classes
- staff.argyll contains good simulations
- Open reference Contains good simulations.
- nrich.maths.org Refer for understanding Pi.
- This is a video showing construction of tangent at any point on a circle
: This is a resource file created by Suchetha, Mathematics teacher, GJC Thyamangondlu
- This is a video showing construction of tangent from external point and theorem
: This is a resource file created by Suchetha, Mathematics teacher, GJC Thyamangondlu
- you want see the kannada videos on theorems and construction of circle click here this is shared by Yakub koyyur GHS Nada.
- Books and journals
- Textbooks
- Syllabus documents (CBSE, ICSE, IGCSE etc)
Learning Objectives
- Appreciation of circle as an important shape as it is an intrical component in the invention of almost everything that we see around us.
- To make students know that circle is a 2-dimensional plane circular figure.
- All points on its edge are equidistant from the center.
- The method of drawing a circle
- The size of the circle is defined by its radius.
- To elicit the difference between a bangle or a circular ring and circle as such.
Teaching Outlines
Concept #1 Introduction to Circle
Source: http://circlesonly.wordpress.com/tag/inventions/
Summary :
The circle is the most primitive and rudimentary of all human inventions, and at the same time, the most dynamic. It is the cornerstone in the foundation of science and technology. It is the basic tool of all engineers and designers. It is used by the greatest artists and architects in the history of mankind. Without a circular shape the wheel, pulleys, gears, ball bearings and a thousand other items we take for granted wouldn’t exist. And of course we would never have the pleasure of driving a car, riding a giant wheel, or watching the moon landing on our television set.
If you look through any old patent claim, you will most likely find the repeated use of circles, spheres, curves, arches, etc. circles are everything and they are nothing. They don’t exist in reality and yet they are the basis of all that mankind has brought into existence. That is why a circle is so fantastic.
Activities
A discussion on “Life without circular shaped figures.”
Discussion based activity to relate and assimilate circular shapes seen in our surroundings.
Circle as a shape
A circle is the set of all points in the plane that are a fixed distance from a fixed point.
Is circle a Polygon ? - A debate
A polygon when increased in number of sides tends to form a circle is shown with this interesting activity.
Concentric circles
Drawing concentric circles, with this hands on activity circle as a shape and variations in it is explored.
Congruent circles
Equal circles are circles with same radius is a concepts that is introduced in this activity.
Equal parts in a circle
Dividing a circle in to parts and exploring to divide it into equal parts is show in this activity.
Pi the mathematical constant
Concept #2 Terms associated with circles
Activities
Centre of a circle
All points on a circle are at fixed distance from a point, which is the center of a circle.
Radius and diameter of a circle
Marking radius and diameter of a circle and understand their relation.
Circumference of a circle
Measuring circumference to understand it as the perimeter of the shape.
Semicircle
Partitioning a circle into two halves to form semicircles by drawing diameter.
Interior and exterior of a circle
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.
Basic elements of a circle
Investigation to understand basic parameters associated with circles.
Chord of a circle
Chords of a circle are of different sizes.The length of the chord increases as it moves closer to the centre and decreases as it moves away from the center.
Arc of a circle
The part of the circumference within the two points in either directions are called its arcs.
Arcs and Sector of a circle
Slice of a circle enclosed between any two radii is called a sector.Semicircle and quadrant are special types of sectors.
Concept #3: Circles and Lines
Activities
Introduction to chords
A chord is the interval joining two distinct points on a circle. This activity investigates formation of chord and compares with the diameter of the circle.
Secant and tangent of a circle
A tangent is a line touching a circle in one point. A secant is the line through two distinct points on a circle.
Concept #4: Theorems and properties
A chord is a straight line joining 2 points on the circumference of a circle.Chords within a circle can be related in many ways.
The theorems that involve chords of a circle are :
- Perpendicular bisector of a chord passes through the center of a circle.
- Congruent chords are equidistant from the center of a circle.
- If two chords in a circle are congruent, then their intercepted arcs are congruent.
- If two chords in a circle are congruent, then they determine two central angles that are congruent.
Activities
Chord length and distance for centre of the circle
For a chord the distance from the center is the perpendicular distance of the chord such that it passes through the center.
The longest chord passes through the centre of the circle
Investigating the diameter is the longest chord of a circle.
Perpendicular bisector of a chord passes through the center of a circle
Since every perpendicular bisector passes through the centre, the centre must lie on every one of them, so the centre must be their single common point.
Congruent chords are equidistant from the center of a circle
In the same circle or in circles of equal radius:
• Equal chords are equidistant from the centre.
• Conversely, chords that are equidistant from the centre are equal.
Angles in a circle subtended by a chord
The angle made at the centre of a circle by the radii at the end points of a chord is called the central angle or angle subtended by a chord at the centre.
Concept #5: Cyclic Quadrilateral
In Euclidean geometry, a cyclic quadrilateral or inscribed quadrilateral is a quadrilateral whose vertices all lie on a single circle. This circle is called the circumcircle or circumscribed circle, and the vertices are said to be concyclic.
Activities
Cyclic quadrilateral
A quadrilateral ABCD is called cyclic if all four vertices of it lie on a circle.In a cyclic quadrilateral the sum of opposite interior angles is 180 degrees.If the sum of a pair of opposite angles of a quadrilateral is 180, the quadrilateral is cyclic.In a cyclic quadrilateral the exterior angle is equal to interior opposite angle.
Properties of cyclic quadrilateral
Relation between the angles of a cyclic quadrilateral are explored with this hand on activity.
Concept #6 Constructions in circles
The students should know that tangent is a straight line touching the circle at one and only point.They should understand that a tangent is perpendicular to the radius of the circle.The construction protocol of a tangent.Constructing a tangent to a point on the circle.Constructing tangents to a circle from external point at a given distance.A tangent that is common to two circles is called a common tangent.A common tangent with both centres on the same side of the tangent is called a direct common tangent.A common tangent with both centres on either side of the tangent is called a transverse common tangent.
Activities
Circles_Constructions
Circles Tangents Problems
Construction of direct common tangent
The direct common tangents to two circles meet on the line of centres and divide it externally in the ratio of the radii.
Construction of transverse common tangent
The transverse common tangents also meet on the line of centres and divide it internally in the ratio of the radii.
Solved problems/ key questions (earlier was hints for problems).
Projects (can include math lab/ science lab/ language lab)
- Collect different types of circular objects
- Collect different Pie Charts.
- Collect different photographs of tools of cutting circles
- Collect different coins of circular shape
- Collect different images of medals
