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Published byArabella May Modified over 6 years ago

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**Place a piece of string round the circle and then open it out flat:**

The circumference is the distance around a circle. Place a piece of string round the circle and then open it out flat: diameter Measure the length of the line: Measure the diameter of the circle. What is the connection between the diameter and the circumference?

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**Measure the distance around the outside of each circle**

Measure the distance around the outside of each circle. Measure the diameter of each circle and complete the table. Circle Circumference Diameter A B C D

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Circle D Circle B Circle A Circle C

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**The circumference is the distance around a circle.**

diameter 1 2 3 0.1 circumference

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**Circumference is equal to roughly 3 x diameter……**

Circumference is equal to roughly 3 x diameter…….and this works or every circle!

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**It’s not easy to use a ruler to measure the distance around a circle.**

A formula for the circumference makes finding it easy. A formula for the connection between the circumference and the diameter is The symbol, , (pi) is said as pie, and is 3.14 (to 2 dp). This is how accurate we need to be on the GCSE calculator paper.

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**How to find circumference given the diameter of a circle**

Find the circumference of the circle below: If you have the diameter: multiply the diameter by 3.14 (). State the formula Substitute the values for p and d.

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**Questions: Given diameter, find the circumference**

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**How to find circumference given the radius**

Find the circumference of the circle below: If you have the radius: multiply this by 2 first to get the diameter. Then multiply the diameter by 3.14 (). State the formula Substitute the values for p and d.

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**Questions:Given radius, calculate the circumference**

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Review

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Answers

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What’s the formula? Calculate the missing numbers in the table below using the circumference formula below. Use 3.14 as an approximation for p. 13.502 6.8 5 C (cm) d (cm) r (cm) 10 31.4 3.4 21.352 2.15 4.3

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Plenary You should know the words used in a circle to include the diameter, radius, circumference and p. Know that p is roughly 3.14. Know and use the formula for the circumference of a circle. or

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**Find the circumference of each circle below.**

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