Find the length of the circumference in terms of pi.

Find the length of the circumference to three significant figures.

Find the length of the circumference to 3 significant figures.

Find the Circumference of a Circle

﻿Hi everyone. I'm Mr. Lund and in this lesson, we're going to find the diameter or the radius of a circle, given the circumference. Hi, everyone. In this question, we're told the circumference of a circle is 23.3 centimetres. We're asked to work out the diameter of the circle in terms of pi. Here's our circle. We're looking for the diameter. Let's start with the formula to find the circumference. Circumference equals pi times by diameter. You have to memorise this for your exam. If I substitute the value of 23.3 into our formula, here's what I'd get. Pi is just a number, so let's divide both sides of this formula by pi. There we go, 23.3 over pi is equal to the diameter. Let's put that on our diagram. There we go. Here's some questions for you to try. Pause to video and return to check your answers. Here's the solutions to question one and two. If you didn't get the right answers, go back and check until you do get the right answers. It's important for the rest of the lesson. If you can work out the diameter of a circle, when given the circumference, it's easy to work out the radius. Here's a circle. We want to work out the radius. Here's our formula, circumference equals pi times by diameter. Let's substitute the value of 40 into our formula. Divide both sides by pi, finds 40 divided by pi equals the diameter. The diameter is 12.732, et cetera. The radius is going to be half that value. So dividing by two, finds the radius. There's our answer to three significant figures. Here's some questions for you to try. Pause the video and return to check your answers. Here are the solutions to questions three. When you are rounding, communicate where you have rounded your answers, especially in exams. It can alter the answers you get. It's easy to make mistakes with more complex calculations. Can you spot the mistakes here? Pause the video and return to check your answers. Here are the solutions to question four. We all make mistakes with mathematics. Being able to spot those mistakes is part of learning. Well done for getting this far. Pause the video and returned to check your answers. Well done for getting this far. Here, you have a larger circle overlapping a smaller circle. It might help to draw the larger circle and the smaller circle separately on a piece of paper to help you with your calculations.

Rearrange the formula that finds the circumference of a circle to make the ‘diameter’ the subject.

The circumference of a circle is 35πcm. What is length of the radius?

The circumference of this circle is 30cm. What is the diameter to 3 significant figures?

The circumference of this circle is 30cm. What is the radius to 3 significant figures?

Find the Diameter or Radius when given the Circumference

In this lesson, we will find the diameter or radius of a circle when given the circumference. This lesson will involve rearranging the formula for the circumference of a circle.

Maths

Y10 Maths (Foundation)

Key Stage 4

Year 10

Circles

Shape and Space (S)

THEME

UNIT

Find the circumference of a circle

Find the Area of a Circle

Find the radius and diameter when given the area

What is missing from this rearranged formula?

What will this formula find?

Find the radius of this circle to three significant figures.

The area of a circle is 20 cm squared. What is the diameter to 3 significant figures?

Find the area of the circle in terms of π.

Find the area of the circle to three significant figures.

Find the area of the circle to 3 significant figures.

Find the area in terms of π.

Lesson overview:Find the Diameter or Radius when given the Circumference

Core Content

Circles: