Lesson Plan Lesosn 5 Calculating Area of Circles

Lesson Plan – Lesosn 5 Calculating Area of Circles Objectives To calculate the area of a circle from the diameter and the radius. . Keywords Circumference, Radius, Diameter, Pi Mental and Oral Starter Pupils to find the circumference of each circle. Main Activity Student to trim the blue squares so that they can fit them inside the circle. They must put the bits they cut off inside the circle as well. They will discover that they can fit 3 blue squares inside the circle with a little bit of space left over. Alternatively this can be shown to pupils using the white board without the pupils actually cutting up the squares. Explain that the radius squared will fit inside the circle a little bit more than three times. Ask them what this reminds them of. They should realise that this the radius squared fits inside the circle Pi times. Explain the formula to pupils. Pupils to work in groups to match each circle to the correct area. Plenary Pupils to use mini white boards to answer the probing questions

LO Finding the Area of a Circle Radius, Diameter, Circumference, Pi Learning Outcomes Level 5 To roughly estimate the area of a circle. Level 6 To calculate the area of a circle using Pi RAG 21 -Nov-20

Level 3 Shape Space Measure I can accurately measure using a tape measure. 4 I can roughly estimate the area of a circle. 5 6 7 /8 I can more accurately estimate the area of a circle. I can calculate the radius, diameter or area of circles and semi circles when given one other measurement. I can calculate volumes and surface area of cylinders. g n i n r e lea r a e w Today I am starting the lesson on level ___________ By the end of this lesson I want to be able to ___________

LO Finding the Area of a Circle Radius, Diameter, Circumference, Pi RAG 22 -Sep-09 Starter Activity Find the Circumference of these circles Radius = 2 cm Radius = 7 cm Diameter = 6 cm

There is a relationship between the radius of a circle and its area.

Look at the radius squared. How many of the radius squared will fit inside the circle?

Use the large blue squares provided. How many can you fit inside the circle? You will have to cut off the edges to fit them inside, the bits you cut off must be put inside the circle too.

Two of these squares will fit easily. Will 3 squares fit?

Three of these squares will fit easily. With a little bit left over. So the Area of the Circle is just over 3 times bigger than the area of the radius squared. What does this remind you of?

Formula for the area of a circle So we can find the area of a circle using the formula. Area of a circle = r 2 x Pi radius Or radius x Pi Area of a circle = πr 2

Today’s Task In your groups match each circle to the correct area.

Area = 78. 55 cm 2 Area = 201. 088 cm 2 Area = ? ? ? Area = 380. 182 cm 2 Area = 132. 7495 cm 2 908. 038 cm 2 Area = 50. 272 cm 2 Area = 283. 5655 cm 2 7. 0695 cm 2

The area of a circle Use π = 3. 14 to find the area of the following circles: 2 cm A = πr 2 = 3. 14 × 22 10 m = 12. 56 cm 2 A = πr 2 23 mm = 3. 14 × 232 = 1661. 06 mm 2 A = πr 2 = 3. 14 × 52 = 78. 5 m 2 78 cm A = πr 2 = 3. 14 × 392 = 4775. 94 cm 2

Probing Questions – Mini White Boards at the Ready What is the minimum information you need to be able to find the circumference and area of a circle? How would you go about finding the area of a circle if you know the circumference?

Success Criteria Level 5 I am working at level 5, I can estimate the area of a circle. Level 6 I am working at level 6, I can calculate the area of a circle using Pi.