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Main parts of the circle

radius. Diameter. Circumference. Main part of a Circle. Main parts of the circle. O. circumference. We can use a ruler to measure the diameter. How can we measure the circumference ?. When doing circle calculations, you will normally use a calculator.

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Main parts of the circle

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  1. radius Diameter Circumference Main part of a Circle Main parts of the circle O www.mathsrevision.com

  2. circumference We can use a ruler to measure the diameter. How can we measure thecircumference?

  3. When doing circle calculations, you will normally use a calculator. This button stores to 8 or 9 decimal places which is more than accurate enough! If your calculator doesn’t have Then use 3.14 instead. The Circumference Some calculators have a button like this: 3.141592654

  4. C = d ALWAYS ASK YOURSELF If you are finding the circumference: 20cm What is the diameter? 20 Then do C= 62.84

  5. C = d C = x 6 Press Then x 6 = Find the Circumference 6cm C = 18.8cm (1 d.p.) What is the diameter? 6

  6. C = d C = x 10 Find the circumference d = 2 x 5 = 10cm 10cm 5cm C = 31.4cm (1 d.p.) What is the diameter? Remember: diameter = 2 x radius 10

  7. The Circumference On your worksheet use to work out the circumference of each circle. C = d

  8. ? ? ? ? ? ? 6 7 8 5 1 2 3 4 ? ? Area of a circle Mathematical Genius! To find the area we could try counting the squares inside the circle… There is a much more accurate way!

  9. r² A = Area of a circle There is a special formula for the area of a circle.

  10. A = r² ALWAYS ASK YOURSELF If you are finding the AREA 10cm What is the RADIUS? 10 Then do A = 314.16

  11. A = r² A = 4² Press Then x 4squared Find the area 4m A = 50.3m² (1 d.p.) What is the RADIUS of this circle? 4

  12. A = r² A = 7² Press Then x 7squared Find the AREA = 7cm ½ x 14 r = A = 153.9cm² (1 d.p.) 7cm ? 14cm What is the RADIUS? 7

  13. A = r² The AREA On your worksheet use to work out the area of each circle.

  14. A = r² A = 12² 24m BONUS r = ½ x 24 = 12m ? 12m A = 452.4m² (1 d.p.) What is the area of this semi-circle? Area of semi-circle = ½ x 452.4 =226.2m² A semicircle is half a circle. First work out area of full circle.

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