Perimeter & Area Video Lecture - for Grade 7

0:0:0: hello students today we have a special
0:0:4: guest with us and his name is
0:0:7: Bob we are on a mission to help Bob find
0:0:10: the area and perimeter of each and
0:0:14: everything in his
0:0:16: room first let's study what area and
0:0:20: perimeter
0:0:22: are the outer boundary of any flat
0:0:25: object is called its
0:0:28: perimeter and the space occupied by that
0:0:32: boundary is called its
0:0:35: area now let's quickly start helping
0:0:40: Bob first Bob has a bed in his
0:0:44: room which shape do you think this
0:0:48: is yes you are correct this is a
0:0:53: rectangle how do you think we can
0:0:56: calculate the space used up by this bet
0:1:0: yes we have to calculate the area of
0:1:3: this
0:1:5: bed now do you remember a rectangle has
0:1:9: two pair of sides of equal
0:1:12: lengths if we Mark the length as
0:1:16: L and breadth as
0:1:20: B then the formula for area of
0:1:24: rectangle is simply length multiplied by
0:1:28: breadth that is is L into
0:1:31: B let's calculate the area now so we
0:1:36: know that length L is equal to 200 cm
0:1:41: and breadth B is equal to 100
0:1:45: cm putting these values in the formula
0:1:48: for area we get L * b equal to 200 *
0:1:56: 100 that is equal to 20,00 000 cm
0:2:2: square now we have to find the perimeter
0:2:5: of this
0:2:6: bed the perimeter will be twice of sum
0:2:11: of length and
0:2:15: breadth do you see the rug near the bed
0:2:19: let's see it
0:2:20: closely do you identify the shape of
0:2:23: this rug let me give you a hint it's a
0:2:26: type of a
0:2:28: quadrilateral yes yes you are correct
0:2:31: it's a
0:2:33: parallelogram we need to help Bob by
0:2:36: calculating the space used up or the
0:2:40: area of this
0:2:42: rug this is the height of the
0:2:45: parallelogram denoted by H and this is
0:2:49: the base length of the parallelogram
0:2:52: denoted by
0:2:53: B what do you think is the formula for
0:2:56: area of a
0:2:58: parallelogram we have already studied a
0:3:1: similar one yes it is also H multiplied
0:3:6: by
0:3:7: B Bob told us the height of the rug is
0:3:10: 50 cm and the base length is 40
0:3:15: cm so to calculate the area we have H =
0:3:20: to 50 cm and B = to 40
0:3:24: cm putting in the formula for the area
0:3:27: of parallelogram that is H * B we get 50
0:3:33: * 40 that is 2, cm square which is the
0:3:41: area of the
0:3:42: rug now Bob is hungry he wants to eat a
0:3:47: sandwich seeing the sandwich he also
0:3:51: wants us to find out about what shape of
0:3:55: the sandwich is and what is its area so
0:3:59: can you identify the shape of the
0:4:2: sandwich yes it's a
0:4:5: triangle now we have to calculate the
0:4:8: area of
0:4:9: triangle if H is the height and B is the
0:4:13: base the area of triangle will be half
0:4:18: multiplied by base multiplied by height
0:4:22: if the height of the triangle is 10
0:4:25: cm and base is 15 cm we get half * 10 *
0:4:34: 15 and finally on solving the area comes
0:4:39: out to be 75 cm
0:4:43: squar also Bob has a round table in his
0:4:47: room let's try to calculate the area and
0:4:51: perimeter of this round table as well
0:4:55: Bob told us that the distance from the
0:4:58: center of the boundary of a circular
0:5:0: table is called the radius and denoted
0:5:4: by
0:5:5: R the formula for area of a circle is
0:5:9: given by pi * radius
0:5:12: square here Pi is a constant whose value
0:5:17: in fraction is taken as 22 by 7 and in
0:5:22: decimal it is taken as
0:5:25: 3.14 if the radius of the table is 20 8
0:5:30: cm the area can be calculated using the
0:5:34: formula pi * radius squar that is equal
0:5:40: to 22x 7 * 28 into
0:5:45: 28 when we solve this the answer comes
0:5:49: out to be
0:5:52: 2,464 CM
0:5:55: squ we have a special word for the
0:5:59: perimeter of a circle that is called as
0:6:2: circumference of a
0:6:4: circle the formula for the circumference
0:6:7: is 2 * < * radius of the circle so
0:6:14: putting the value of radius and Pi we
0:6:18: get 2 * 22 upon 7 *
0:6:24: 28 upon solving this we get the
0:6:28: circumference of this circular table
0:6:30: equal to
0:6:32: 176
0:6:34: cm so we have studied that perimeter of
0:6:37: a rectangle is twice multiplied by
0:6:41: length plus
0:6:42: breadth area of rectangle is length
0:6:46: multiplied by
0:6:48: breadth area of parallelogram is height
0:6:52: multili by
0:6:54: base area of circle is pi * radius
0:6:59: Square where Pi is a constant and whose
0:7:3: value is taken as 22 upon 7 or
0:7:9: 3.14 and lastly the circumference or the
0:7:13: perimeter of the circle is 2 * piun *
0:7:18: the radius of the
0:7:21: circle we hope that you have understood
0:7:24: the concept of area and perimeter now
0:7:27: here's a secret on how you can study
0:7:30: effectively with the edurev app you can
0:7:33: learn with chapter notes watch video
0:7:36: lectures and solve ncrt based McQ tests
0:7:40: of this chapter on edurev and that's not
0:7:43: all you also get amazing courses for
0:7:46: class 7th and much more for your class
0:7:49: 7th preparation thank you