3D shapes, volume and surface area
खेलकर सीखें
इन सवालों के जवाब देकर एनर्जी कमाएं, फिर मछली पकड़ें और घूमें। कोई अकाउंट नहीं चाहिए।
लेसन नोट्स
Faces, Edges and Vertices
- A face is a flat surface of a 3D shape.
- An edge is a line where two faces meet.
- A vertex (plural: vertices) is a point where edges meet.
- For a cuboid: 6 faces, 12 edges, 8 vertices.
- For a cube: 6 faces, 12 edges, 8 vertices.
- For a cylinder: 3 faces (2 circular, 1 curved), 2 edges, 0 vertices.
- For a sphere: 1 curved face, 0 edges, 0 vertices.
- For a square-based pyramid: 5 faces, 8 edges, 5 vertices.
Nets of 3D Shapes
- A net is a 2D shape that folds up to make a 3D shape.
- A cube net is made of 6 squares.
- A cuboid net is made of 6 rectangles (3 pairs of identical rectangles).
- A cylinder net is made of 2 circles and 1 rectangle.
- A square-based pyramid net is made of 1 square and 4 triangles.
- A triangular prism net is made of 2 triangles and 3 rectangles.
Plans and Elevations
- A plan is the view from above (bird's-eye view).
- A front elevation is the view from the front.
- A side elevation is the view from the side.
- Plans and elevations are 2D drawings that show the shape of a 3D object from different directions.
- They are used in design and architecture to describe 3D objects accurately.
Volume of Cubes and Cuboids
- Volume is the amount of space inside a 3D shape.
- Volume is measured in cubic units, e.g. cm3, m3.
- Volume of a cube: V = s3, where s = side length.
- Volume of a cuboid: V = l × w × h, where l = length, w = width, h = height.
- Example: a cuboid with l = 5 cm, w = 3 cm, h = 2 cm has V = 5 × 3 × 2 = 30 cm3.
Volume of Prisms
- A prism is a 3D shape with the same cross-section all along its length.
- Volume of a prism: V = A × l, where A = area of cross-section, l = length.
- The cross-section is the shape you see when you slice the prism parallel to its base.
- Example: a triangular prism with cross-section area 12 cm2 and length 10 cm has V = 12 × 10 = 120 cm3.
- Cubes and cuboids are special types of prism.
Volume of Cylinders
- A cylinder is a prism with a circular cross-section.
- Volume of a cylinder: V = π r2 h, where r = radius, h = height.
- Example: a cylinder with r = 3 cm and h = 10 cm has V = π × 32 × 10 = 90π cm3 ≈ 282.7 cm3.
- Use π ≈ 3.14 or the π button on your calculator.
Surface Area of Cuboids
- Surface area is the total area of all the faces of a 3D shape.
- Surface area is measured in square units, e.g. cm2, m2.
- A cuboid has 6 rectangular faces; opposite faces are identical.
- Surface area of a cuboid: SA = 2(lw + lh + wh), where l = length, w = width, h = height.
- Example: a cuboid with l = 5 cm, w = 3 cm, h = 2 cm has SA = 2(5×3 + 5×2 + 3×2) = 2(15 + 10 + 6) = 62 cm2.
Surface Area of Prisms
- To find the surface area of a prism, add the areas of all its faces.
- For a prism, the two end faces are identical (the cross-section).
- The other faces are rectangles; their total area is perimeter of cross-section × length.
- Surface area of a prism: SA = 2A + P × l, where A = area of cross-section, P = perimeter of cross-section, l = length.
- Example: a triangular prism with cross-section area 12 cm2, perimeter 16 cm, length 10 cm has SA = 2×12 + 16×10 = 24 + 160 = 184 cm2.
Surface Area of Cylinders
- A cylinder has 2 circular faces and 1 curved surface.
- The curved surface unfolds into a rectangle with width = circumference of the circle (2πr) and height = h.
- Surface area of a cylinder: SA = 2πr2 + 2πrh, where r = radius, h = height.
- Example: a cylinder with r = 3 cm and h = 10 cm has SA = 2π×32 + 2π×3×10 = 18π + 60π = 78π cm2 ≈ 245.0 cm2.
Capacity and Litres
- Capacity is the amount a container can hold.
- Capacity is often measured in litres (L) or millilitres (mL).
- 1 litre = 1000 millilitres.
- 1 litre = 1000 cm3.
- 1 millilitre = 1 cm3.
- 1 m3 = 1000 litres.
- To convert from cm3 to litres, divide by 1000.
- To convert from litres to cm3, multiply by 1000.
स्लाइड्स
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प्रैक्टिस सवाल
फ्री प्रीव्यू — 65 में से 8 सवाल। सभी देखने के लिए साइन अप करें।
1.Which of these is an SI derived unit of volume?
Easy- Acubic metre
- Bkilogram
- Cnewton
- Dmetre
2.The volume of a container is generally understood to be its capacity. Which statement describes capacity?
Easy- AThe amount of fluid the container could hold
- BThe amount of space the container itself displaces
- CThe total length of all its edges
- DThe total area of all its faces
3.A cube has edge length 1 dm. What is its volume in litres?
Easy- A1 litre
- B10 litres
- C0.1 litres
- D1000 litres
4.A cuboid has length 5 cm, width 4 cm and height 3 cm. What is its volume?
Medium- A60 cm3
- B12 cm3
- C47 cm3
- D94 cm3
5.A prism has a cross-sectional area of 12 cm2 and a length of 9 cm. What is its volume?
Medium- A108 cm3
- B21 cm3
- C54 cm3
- D216 cm3
6.A cylinder has radius 3 cm and height 10 cm. Using π = 3.14, what is its volume to 1 decimal place?
Medium- A282.6 cm3
- B94.2 cm3
- C188.4 cm3
- D565.2 cm3
7.A cuboid has length 8 cm, width 5 cm and height 2 cm. What is its total surface area?
Medium- A132 cm2
- B80 cm2
- C66 cm2
- D264 cm2
8.A cylinder has radius 4 cm and height 7 cm. Using π = 3.14, what is its total surface area to 1 decimal place?
Hard- A276.3 cm2
- B175.8 cm2
- C351.7 cm2
- D100.5 cm2
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