Page 74 - WCS - Electrical

WORKSHOP CALCULATION & SCIENCE - CITS

θ = Angle of sector of circle
l = Arc length
r = radius

Length of Arc l = θ x 2πr unit
360°
Perimeter P = 2r + l unit
θ lr
Area = x πr² unit² (or) A = unit²
360° 2

1 Find the perimeter and area of a sector of circle of radius 7 cm and its angle is 120°.

Given:
Angle of sector of circle = 120°
Radius = 7 cm
To find:

Perimeter = ? , Area = ?
Solution:

Length of arc (l) = θ x 2πr unit
360°
120 22
= x 2 x x 7 cm
360 7
= 14.67 cm
Perimeter = 2r +l unit

= 2 x 7 + 14.67 cm
= 28.67 cm
Area = θ x πr² unit²
360°
120° 22
Area = x x 7 cm² = 51.33 cm²
360° 7

2 Find the radius of the circle if the angle is 60° and the area of a sector of a circle is 144 cm²,

Given:

Area of sector of circle (A) = 144 cm²
Angle of sector of circle θ = 60°

To find:
Radius of circle = ?

Solution:
θ
Area (A) = x πr² unit²
360°

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CITS : WCS - Electrical - Exercise 5