TECHNICAL DRAWING SECOND TERM LESSON NOTE

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 TECHNICAL DRAWING SECOND TERM LESSON NOTE

SECOND TERM E-LEARNING NOTE

SUBJECT:TECHNICAL DRAWING

CLASS:SS1

TITLE:SECOND TERM SCHEME OF WORK

 

WEEK 1:    Revision of the work for last term. Inscribed and circumscribed.

WEEK 2     Escribed circle.

WEEK 3:Polygons

WEEK 4:    Plain scales

WEEK 5:    Diagonal and chordalScales

WEEK 6:   Enlargement and reduction of plain figures

WEEK 7:    Enlargement and reduction of plain figures

WEEK 8:    Equal area of figures

WEEK 9:    Equal area of figures

WEEK 10:  Tangency

WEEK 11.Revision and Examination.

 

Reference materials:

Technical drawing by J.N. Green.

Engineering drawing 1 by M.A.Parker and F.Pickup

Metal work technology by G.H. Thomas.

Drafting Technology and practice by William P. Spence

Technical Drawing by F.B Mayock( 1- 4 )

Basic technology for junior secondary schools book 1 by G.N Nneji, E.J. Okon, V.C. Nwachukwu, N.A. David, and T.C. Ogbuanya.Pages 1-17, 34-78.

Basic technology for junior secondary schools book 2 by I. Elekwa , O.A. Bamiro, A.O. Oluyide,

D.L Ladoye, A. Nurudeen and I.O. Akuru

Technical drawing for senior secondary schools by Y.A Thanni and C.A Faseun-Motesho Pages 97-103

 

 TECHNICAL DRAWING SECOND TERM LESSON NOTE

WEEK ONE                                                                                                   DATE:………………

Revision of last term work. Inscribed and circumscribed circles

                       

Content:

(i)  Inscribed circles.

(ii) Circumscribed circles 

Inscribed circles

Example 1   To inscribe a circle in a given triangle.

Method:

(i)  Draw the given equilateral triangle.

(ii) Bisect any two of the angles e.g X and Y to obtain the centre of the triangle, O.

(iii)  Draw a line from Z through O to B.

(iv)  Bisect angle OBC to obtain the centre of one of the circles, A.

(v)   With O as centre and radius OA, locate the centres 1 and 2 of the remaining two circles.

(vi)  Drop a perpendicular from A which meets line XB at point C. AC is the radius of the three circles.

(vii) With compass pin at points A, 1 and 2 in turn, draw the three circles.

 

Example 3To inscribe a circle in any sector.

Method:

(i)  Bisect the vertical angle R. This angular bisector meets the arc of the sector at point S.

(ii) Construct a tangent at point S.

(iii)Extend the radius of the sector to meet the tangent at points P and Q.

(iv)Bisect one of the base angles e.g< RQS to obtain the centre of the circle, O.

(v) With O as centre and radius OS, draw the required circle.

Example 4To inscribe a circle in any regular polygon, rhombus or deltoid(kite).

TECHNICAL DRAWING SECOND TERM LESSON NOTE

Method:

(i)  Bisect any two angles of the given polygon. The two bisectors meet at a point O.

(ii) Point O is the centre of the circle. Drop a perpendicular from O to any side of the polygon, ie OD.

(iii)With O as centre and radius OD, draw the required circle.

 

Evaluation Questions

1.  A triangle ABC stands on side AB as base and has the following dimensions: AB = 60mm, AC = 50mm

and angle CAB = 670. Construct the triangle and draw a circle in it.

2.  Construct a regular polygon whose side is of length 40mm. Draw a circle in it to touch all the sides. 

 

 

Circumcribedcircles

 

Example 1  To circumscribe a circle on a triangle or inscribe a triangle in a circle

Method:

(i)   Draw the given triangle ABC.

(ii)  Bisect any two sides of the triangle ie AC and BC, These bisectors intersect at point O.

(iii) With O as centre and radius OA or OB or OC, draw a circle to pass through the three points.

 

Evaluation Questions

 

1.  Construct a triangle ABC on AB as base with AB = 70mm, AC = 57mm and BC = 76mm. Circumscribe a

circle on it.

2.  Construct a triangle ABC with side AB = 70mm, AC = 90mm and < ABC = 1050. Circumscribe a circle

on it.

 

General evaluation/revisionalquestions

 

1.  A triangle has a perimeter 130mm, base 40mm and a base angle 1050. (i) Construct the triangle.

(ii)  Measure and state the other base angle. (WAEC)

2.  Construct a triangle PQR with base = 70mm, vertical height = 50mm and vertical angle = 550

 (WAEC)

3.  Construct a triangle whose perimeter is 120mm and of sides in the ratio 3:4:5. (WAEC).

4.  Construct a triangle of sides AB = 60mm, AC = 55mm and < ABC = 600. Construct a triangle similar

to this and whose perimeter is 140mm.

5. Inscribe an octagon in a square of side 80mm.

 

Method:

(i)  Draw the given polygon and join opposite corners as shown above.

(ii) Bisect external angles P23 and S32 whose bisectors meet at point O, the centre of the circle.

(iii)Drop a perpendicular, OD to side 2-3. This is the radius of the circle.

(iv)With O as centre and radius OD, draw a circle. Repeat the above procedure for each side and circle.

 

Evaluation Questions

1.   Escribe a circle on a triangle of sides AB = 55mm, AC = 60mm and BC = 50mm.

2  . A regular hexagon has its sides 50mm long. Draw the hexagon and describe circles about it.

 TECHNICAL DRAWING SECOND TERM LESSON NOTE

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