7th Maths : Term 3 Unit 4 : Geometry : Construction of circles and concentric circles : Exercise 4.2 : Text Book Back Exercises Questions with Answers, Solution

**Exercise
4.2**

**1. Draw circles for the following measurements
of radius (r)/ diameters(d).**

**(i) r = 4 cm**

**(ii) d = 12 cm**

**(iii) r = 3.5 cm**

**(iv) r = 6.5 cm.**

**(v) d = 6 cm**

**Solution: **

**(i) r = 4cm**

**Step 1 :** Market a point ‘O’ on the paper.

**Step 2 :** Extended the compass distance equal to radius 4 cm.

**Step 3 :** At center ‘O’, helded the compass firmly and placed the pointed
end of the compass.

**Step 4 :** Slowly rotated the compass around to get the circle.

**(ii) d =12cm **

given *d *= 12 cm

∴ radius* r* = *d*/2 = 12/2 = 6 cm

**Step 1 :** Market a point ‘O’ on the paper.

**Step 2 :** Extended the compass distance equal to radius 6 cm.

**Step 3 : **At center ‘O’, held the compass firmly and placed the pointed
end of the compass.

**Step 4 :** Slowly rotated the compass around to get the circle.

**(iii) r = 3.5cm**

**Step 1 :** Market a point ‘O’ on the paper.

**Step 2 :** Extended the compass distance equal to radius 3.5 cm.

**Step 3 : **At center ‘O’, held the compass firmly and placed the pointed
end of the compass.

**Step 4 :** Slowly rotated the compass around to get the circle.

**(iv) r = 6.5 cm**

**Step 1 :** Market a point ‘O’ on the paper.

**Step 2 :** Extended the compass distance equal to radius 6.5 cm.

**Step 3 :** At center ‘O’, held the compass firmly and placed the pointed
end of the compass.

**Step 4 :** Slowly rotated the compass around to get the circle.

**(v) d = 6 cm**

∴ radius *r* = *d* / 2 = 6 / 2 = 3 cm

**Step 1 :** Market a point ‘O’ on the paper.

**Step 2 : **Extended the compass distance equal to radius 3 cm.

**Step 3 :** At center ‘O’, held the compass firmly and placed the pointed
end of the compass.

**Step 4 :** Slowly rotated the compass around to get the circle.

**2. Draw concentric circles for the following
measurements of radii / diameters. Find out the width of each circular ring.**

**(i) r = 3 cm and r = 5 cm.**

**(ii) r = 3.5 cm and r = 6.5 cm.**

**(iii) d = 6.4 cm and d = 11.6 cm.**

**(iv) r = 5 cm and r = 7.5 cm.**

**(v) d = 6.2 cm and r = 6.2 cm.**

**(vi)
r = 7.1 cm and d = 12 cm.**

**Solution: **

**(i) r = 3 cm and r = 5 cm**

Width of the circular ring = OB – OA = 5 – 3 = 2 cm

**Step 1 :** Drawn a rough diagram and market the given measurements

**Step 2 :** Taken any point O and marked it as the center.

**Step 3 :** With O as center drawn a circle of radius OA = 3 cm.

**Step 4 :** With O as center drawn a circle of radius OB = 5 cm. Thus the
concentric circles C_{1} and C_{2} are drawn.

Width of the circular ring = OB – OA = 5 –3 = 2 cm

**(ii) r = 3.5 cm and r = 6.5 cm**

**Step 1 :** Drawn a rough diagram and market the given measurements

**Step 2 :** Taken any point O and marked it as the center.

**Step 3 :** With O as center drawn a circle of radius OA = 3.5 cm.

**Step 4 :** With O as center drawn a circle of radius OB = 6.5 cm. Thus the
concentric circles C_{1} and C_{2} are drawn.

Width of the circular ring = OB – OA = 6.5 –3.5 = 3 cm

** (iii) d
= 6.4 cm and d = 11.6 cm.**

*r* = *d */ 2

∴ *r*
= 6.4 / 2 = 3.2 cm ; * r*
= 11.6 / 2 = 5.8 cm

**Step 1 :** Drawn a rough diagram and market the given measurements

**Step 2 :** Taken any point O and marked it as the center.

**Step 3 :** With O as center drawn a circle of radius OA = 3.2 cm.

**Step 4 : **With O as center and drawn a circle of radius OB = 5.8 cm. Thus
the concentric circles C_{1}and C_{2} are drawn.

Width of the circular ring = OB – OA = 5.8 – 3.2 = 2.6 cm

**(iv) r = 5 cm and r = 7.5 cm. **

**Step 1 :** Drawn a rough diagram and market the given measurements

**Step 2 : **Taken any point O and marked it as the center.

Step 3 : With O as center drawn a circle of radius OA = 5 cm.

**Step 4 : **With O as center drawn a circle of radius OB = 7.5 cm. Thus the
concentric circles C_{1} and C_{2} are drawn.

Width of the circular ring = OB – OA = 7.5 – 5 = 2.5 cm

**(v) d = 6.2 cm and r = 6.2 cm.**

* r* = *d*/2

∴ *r*
= 6.2 / 2 = 3.1 cm and* r* = 6.2 cm

**Step 1 : **Drawn a rough diagram and market the given measurements

**Step 2 : **Taken any point O and marked it as the center.

**Step 3 : **With O as center, drawn a circle of radius OA =3.1 cm.

**Step 4 : **With O as center, drawn a circle of radius OB = 6.2 cm. Thus concentric
circles C_{1} and C_{2} are drawn.

Width of the circular ring = OB – OA = 6.2 – 3.1 = 3.1 cm

**(vi) r = 7.1 cm and d = 12 cm.**

*r *= *d*/2

∴ *r
*= 12/2 = 6 cm and *r* = 7.1 cm

Step 1 : Drawn a rough diagram and marked the given measurements

Step 2 : Taken any point O and marked it as center.

Step 3 : With O as center, drawn a circle of radius OA = 6 cm.

**Step 4 :** With O as center, drawn a circle of radius OB = 7.1 cm. Thus
concentric circles C_{1 }and C_{2} are drawn.

Width of the circular ring = OB – OA = 7.1 – 6 = 1.1 cm

Tags : Questions with Answers, Solution | Geometry | Term 3 Chapter 4 | 7th Maths , 7th Maths : Term 3 Unit 4 : Geometry

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7th Maths : Term 3 Unit 4 : Geometry : Exercise 4.2 (Construction of circles and concentric circles) | Questions with Answers, Solution | Geometry | Term 3 Chapter 4 | 7th Maths

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