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GenX-Education
  • 7/27/2024
Transcript
00:00Hi kids! Today we will learn about circles, so let's get started.
00:08Kids, we know it's a circle.
00:12Now, we will learn more things about a circle,
00:18like center of a circle, radius of a circle, diameter of a circle,
00:26chord, arc, and circumference of a circle.
00:31So let's start.
00:36Circle is a 2D figure which is formed of points equidistant from the center.
00:44This is the center of the circle.
00:48That is, circle is made up of points which are all at equal distance from the center.
00:57And all the points are at equal distance from the center in a circle.
01:04Now let's learn what is a radius.
01:09A radius is a straight line from the center of circle to the boundary of a circle.
01:17Or, radius is a distance between the boundary of the circle and the center of the circle.
01:26Let's draw any line from the center to the boundary.
01:32It will be a radius.
01:36You can draw any number of radius.
01:40Now let's learn what is a diameter.
01:44Straight line that divides the circle in exactly two parts is known as a diameter.
01:52It is also two times the radius.
01:56Now, let's learn what is a chord.
02:01A straight line whose both end points lie on the circle is called the chord of a circle.
02:10Here, A, B, C, D, E, F are all chords of this circle.
02:18We can make any number of chords.
02:23Longest chord is a chord that passes through the center of a circle, that is, the diameter.
02:31Diameter is the longest chord of the circle.
02:36Now, let's learn what is circumference.
02:41Circumference is the boundary of a circle.
02:45All these figures are showing circumference of the circle.
02:51Now, let's learn what is an arc.
02:55Any small or big portion of the circumference is called arc of the circle.
03:02All these figures are representing arcs.
03:06Some are smaller portions of circle and some bigger portions, but all are arcs of different sizes.
03:15So, kids, we learned about a circle, its radius, diameter, chord, arc, and circumference.
03:25Now, let's learn how we can find out the circumference of a circle.
03:31We know circumference is a distance around the boundary of the circle, like its perimeter of a square.
03:41For a circle, it's a circumference.
03:45If we have a circle and we know its radius, we can find its circumference by using the formula 2 pi r, where pi equals 3.14.
04:02Let's take an example.
04:05Here we have a circle and we are given with its radius. It is 9 centimeters.
04:13Let's find out the circumference of this circle.
04:18We know circumference equals 2 pi r, that is, 2 multiplied by pi multiplied by r.
04:30We have r equals 9 centimeters and pi equals 3.14.
04:39So, circumference equals 2 multiplied by 3.14 multiplied by 9, which will give us 56.52 centimeters.
04:53So, circumference of this circle equals 56.52 centimeters.
05:01Now, let's find out the circumference of this circle.
05:07We know circumference equals 2 pi r, that is, 2 multiplied by pi multiplied by r.
05:19We have radius equals 3 centimeters in this circle and pi is always equal to 3.14.
05:31So, here we have circumference equal to 2 multiplied by 3.14 multiplied by 3.
05:42So, here it will give us 18.84 centimeters.
05:49So, circumference of the circle with radius 3 centimeters is 18.84 centimeters.
05:59Now, we know how to find out the circumference of the circle.
06:06Now, let's learn how we can calculate the area of a circle.
06:12Area of a circle is the area inside the circumference of a circle.
06:18We can find the area of circle by using the formula pi r squared, that is, pi multiplied by r multiplied by r.
06:32Now, let's take an example.
06:36Here we have a circle and its radius is given, which is 3 centimeters.
06:43We know area of circle is pi r squared.
06:49So, we will write it as area of circle equals 3.14 multiplied by r squared, that is, 3 multiplied by 3.
07:03Now, 3.14 multiplied by 3 multiplied by 3, that is, 3.14 multiplied by 9, it will give us 28.26.
07:20So, the area of this circle is 28.26 centimeters square, as area is always mentioned in square units.
07:31So, kids, today we learned a lot about circles.
07:36Now, you may go ahead and take a quiz to learn more.
07:40Bye-bye.