Lesson Plan – Lesosn 5 Calculating Area of Circles

Mental and Oral StarterPupils to find the circumference of each circle.

Main ActivityStudent 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.

PlenaryPupils to use mini white boards to answer the probing questions

ObjectivesTo calculate the area of a circle from the diameter and the radius..

KeywordsCircumference, Radius, Diameter, Pi

20 Apr 2023

RAG

Radius, Diameter, Circumference, Pi

LO Finding the Area of a Circle

Learning Outcomes

Level 5To roughly estimate the area of a circle.

Level 6To calculate the area of a circle using Pi

Level 3 4 5 6 7 /8ShapeSpaceMeasure

I can accurately measure using a tape measure.

I can roughly estimate the area of a circle.

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.

Today we are learning

I am starting the lesson on level _____________________

By the end of this lesson I want to be able to _____________________

22-Sep-09

RAG

Radius, Diameter, Circumference, PiLO Finding the Area of a Circle

Starter ActivityFind the Circumference of these circles

Radius = 7cm

Diameter = 6cm

Radius = 2cm

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.

radius

Area of a circle = πr2Area of a circle = πr2

Area of a circle = r 2 x Pi

Or radius x radius x Pi

Today’s Task

In your groups match each circle to the correct area.

Area = 78.55cm2

Area = 201.088cm2

Area = ???????????

Area = 380.182cm2

Area = 132.7495cm2

Area = 908.038cm2

Area = 50. 272cm2

Area = 283.5655cm2

Area = 7.0695cm2

The area of a circle

Use π = 3.14 to find the area of the following circles:

A = πr22 cm

= 3.14 × 22

= 12.56 cm2

A = πr2

10 m= 3.14 × 52

= 78.5 m2

A = πr2

23 mm = 3.14 × 232

= 1661.06 mm2

A = πr2

78 cm= 3.14 × 392

= 4775.94 cm2

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?

Probing Questions – Mini White Boards at the Ready

Success Criteria

Level 5I am working at level 5, I can estimate the area of a circle.

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