Mathematics Chapter 10 Visualising Solid Shapes
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    NCERT Solution For Class 8 Social%2525252525252bscience

    Visualising Solid Shapes Here is the CBSE Social%2525252525252bscience Chapter 10 for Class 8 students. Summary and detailed explanation of the lesson, including the definitions of difficult words. All of the exercises and questions and answers from the lesson's back end have been completed. NCERT Solutions for Class 8 Social%2525252525252bscience Visualising Solid Shapes Chapter 10 NCERT Solutions for Class 8 Social%2525252525252bscience Visualising Solid Shapes Chapter 10 The following is a summary in Hindi and English for the academic year 2021-2022. You can save these solutions to your computer or use the Class 8 Social%2525252525252bscience.

    Question 1
    CBSEENMA8003294
    Question 3
    CBSEENMA8003296

    Let there be a combination of three cubes, one on the top of the other as shown in the adjoining figure. What will be its top and side view?

    Solution
    (i) If we look at this solid structure from the top, we would see just a square.

    (ii) If we look at it from a side, i.e. left or right, then we would see a figure as shown here.

    Note: In this case the front view would also be the same.
    Question 4
    CBSEENMA8003297

    Look at the combination of four cubes as shown in the adjoining figure. Show its various views.

    Solution
    The side view, front view and the top view of above solid are as given below:
    Question 13
    CBSEENMA8003306
    Question 15
    CBSEENMA8003308
    Question 16
    CBSEENMA8003309

    What happens to F, V and E if some parts are sliced off from a solid? (To start with, you may take a plasticine cube, cut a corner off and investigate).

    Solution
    Consider the following cuboid ABCDEFGH:

    Case I: The given cuboid has:
    (i) Number of faces (F) = 6
    (ii) Number of vertices(V) = 8
    (iii) Number of edges (E) = 12
    We have,                    F + V = 6 + 8 = 14
                            F + V - E = 14 - 12 = 2
    i.e.                   F + V - E = 2
    or the Euler's formula is verified.
    Case II: [A part is sliced off]

    We have:
             Number of faces (F) = 7
         Number of vertices (V) = 10
            Number of Edges (E) = 15
     Also,                                 F + V = 7 + 10 = 17
    and                                F + V - E = 17 - 15 = 2
         Here also, Euler's formula holds true.


    Question 17
    CBSEENMA8003310

    Can a polyhedron have for its faces 3 triangles?

    Solution
    A polyhedron is bounded by four or more than four polygonal faces. No, it is not possible that a polyhedron has 3 triangles for its faces.

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    Question 18
    CBSEENMA8003311

    Can a polyhedron have for its faces 4 triangles?

    Solution
    A polyhedron is bounded by four or more than four polygonal faces. Yes, 4 triangles can be the faces of a polyhedron.
    Question 19
    CBSEENMA8003312

    Can a polyhedron have for its faces a square and four triangles?

    Solution
    A polyhedron is bounded by four or more than four polygonal faces. Yes, a square and 4 triangles can be the faces of a polyhedron.
     
    Question 20
    CBSEENMA8003313

    Is it possible to have a polyhedron with any given number of faces? (Hint: Think of a pyramid).

    Solution
    Yes, it can be possible only if the number of faces is four or more than four.
    Question 21
    CBSEENMA8003314

    Which are prisms among the following?

    Solution

    Since, a prism is a polyhedron having two of its faces congruent and parallel, where as other faces are parallelogram.
    ∴ (i) No, a nail is not a prism.
       (ii) Yes, unsharpened pencil is a prism.
       (iii) No, table weight is not a prism.
        (iv) Yes, box is a prism.

    Question 22
    CBSEENMA8003315

    How are prisms and cylinders alike?

    Solution
    Both of the prisms and cylinders have their base and top as congruent faces and parallel to each other. Also, a prism becomes a cylinder as the number of sides of its base becomes larger and larger.
    Question 23
    CBSEENMA8003316

    How are pyramids and cones alike?

    Solution
    The pyramid and cones are alike becomes their lateral faces meet at a vertex. Also, a pyramid becomes a cone as the number of sides of its base becomes larger and larger.
    Question 24
    CBSEENMA8003317

    Is a square prism same as a cube? Explain.

    Solution
    No, not always, because it can be a cuboid also.
    Question 25
    CBSEENMA8003318

    Verify Euler’s formula for these solids.


    Solution
    (i) In figure (i), we have
                                        F = 7,  V = 10  and E = 15
    ∴                              F + V = 7 + 10 = 17
                   F + V - E = 17 - 15 = 2
    i.e.          F + V - E = 2
    Thus, Euler's formula is verified.
    (ii) In figure (ii), we have
                                F = 9, V = 9 and E = 16
    ∴                  F + V = 9 + 9 = 18
           and          F + V - E = 18 - 16 = 2
            i.e.          F + V - E = 2
    Thus, Euler's formula is verified.
    Question 26
    CBSEENMA8003319

    Using Euler’s formula find the unknown.

    Solution
    (i) Here, V = 6 and E = 12
    Since                     F + V - E = 2
    ∴                           F + 6 - 12 = 2
    or                                 F - 6 = 2
    or                                 F = 2 + 6 = 8
    (ii) Here, F = 5 and E = 9
    Since                             F + V - E =  2
    or                                   5 + V - 9 = 2
    or                                          V - 4 = 2
    or                                           V = 2 + 4 = 6
    (iii) Here F = 20 and V = 12
    Since,                            F + V - E = 2
    ∴                                   20 + 12 - E = 2
    or                                   20 + 12 - E = 2
                                                 32 - E = 2
    or                                                 E = 32 - 2 = 30
    Question 27
    CBSEENMA8003320

    Can polyhedron have 10 faces, 20 edges and 15 vertices?

    Solution

    Here, F = 10, E = 20 and V = 15
    We have:
                                F + V - E = 2
    ∴                    10 + 15 - 20 = 2
    or                            25 - 20 = 2
    or                                  5 = 2 which is not true
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         Thus, such a polyhedron is not possible.

    Question 29
    CBSEENMA8003322
    Question 33
    CBSEENMA8003326

    Define the following:
    (i) Polyhedron    (ii) Prism     (iii) Pyramid

    Solution

    (i) Polyhedron: A solid shapes bounded by polygons is called a polyhedron. For example, cube, cuboid, etc.
    (ii) Prism: A prism is a solid, whose faces are parallelograms and whose ends (or bases) are congruent parallel rectilinear figures.
    (iii) Pyramid: A pyramid is a polyhedron whose base is a polygon of any number of sides and whose other faces are triangles with a common vertex.

    Question 34
    CBSEENMA8003327

    What is a polyhedra?

    Solution
    The plural of polyhedron is called polyhedra.
    Question 35
    CBSEENMA8003328

    What is a tetrahedron?

    Solution
    If the base of a pyramid is a triangle, then we call it as a tetrahedron.
    Question 36
    CBSEENMA8003329

    What is a parallelopiped?

    Solution
    When the ends of a quadrilateral prism are parallelograms, then it is called a parallelopiped.
    Question 37
    CBSEENMA8003330

    Which of the following solids are not polyhedrons?

    Solution

    (i) A cylinder is not a polyhedron.
    (ii) A cuboid is a polyhedron.
    (iii) A cube is a polyhedron.
    (iv) A cone is not a polyhedron.
    (v) A sphere is not a polyhedron.
    (vi) A pyramid is a polyhedron.

    Question 38
    CBSEENMA8003331

    Why the following solids are not polyhedron?
    (i) A sphere.
    (ii) A cone.
    (iii) A cylinder.

    Solution
    Since, a polyhedron is a solid shape bounded by polygons. However, (i) a sphere, (ii) a cone and (iii) a cylinder are not polyhedron because they are made of polygons, i.e. their faces are not polygons.
    Question 39
    CBSEENMA8003332

    Name the following polyhedron.



    How many faces, vertiecs and edges of this solid are there?

    Solution

    ∵ The ends (bases) of the given solid are congruent rectilinear figure each of six sides.
    ∴ It is a hexagonal prism.
    In a hexagonal prism, we have:
    The number of faces = 8
    The number of edges = 18
    The number of vertices = 12

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    Question 40
    CBSEENMA8003333

    What Euler’s formula? Verify the Euler’s formula for a pentagonal prism.

    Solution

    If a polyhedron is having number of faces as F, number of edges as E and the number of vertices as V, then the relationship F + V = E + 2 is known as Euler’s formula. Following figure is a solid pentagonal prism.

    It has:
     Number of faces (F) = 7
     Number of edges (E) = 15
     Number of vertices (V) = 10
    Substituting the values of F, E and V in the relation,
                         F + V = E + 2
    we have  
                         7 + 10 = 15 + 2
    rightwards double arrow                     17  = 17
    Which is true, the Euler’s formula is verified. 

    Question 41
    CBSEENMA8003334

    A polyhedron is having 8 vertices and 12 edges. How many faces of it are there?

    Solution

    Number of vertices (V) = 8
       Number of edges (E) = 12
    Let the number of faces = V
    Now, using the Euler's formula
                       F + V = E + 2
    we have
                       F + 8 = 12 + 2
    rightwards double arrow              F + 8 = 14
    rightwards double arrow                  F =  14 - 8 
    rightwards double arrow                 F = 6
      Thus, the required number of faces = 6.

    Question 42
    CBSEENMA8003335

    A dodecahedron is having 20 vertices and 30 edges. How many faces are there?

    Solution

    Here:
      Number of vertices (V) = 20
         Number of edges (E) = 30
    Let the number of faces are F. Then using Euler's formula, we have
                      F + V = E + 2                                                      ...(1)
    ∴         Substituting the values of V and E in (1), we get
                       F + 20 = 30 + 2
    rightwards double arrow              F + 20 = 32
    rightwards double arrow                     F = 32 - 20
    rightwards double arrow                     F = 12
       Thus, the required number of faces = 12.

    Question 43
    CBSEENMA8003336

    An icosahedron is having 20 triangular faces and 12 vertices. Find the number of its edges.

    Solution

    Here:
                   Number of faces (F) = 20
                  Number of vertices (V) = 12
    Let the number of edges be E.
    ∴  Using Euler's formula, we have
                               F + V = E + 2
    rightwards double arrow                  20 + 12 = E + 2 
    rightwards double arrow                         32  = E + 2
    rightwards double arrow                            E  = 32 - 2 = 30
        Thus, the required number of edges = 30.
     
     

    Question 44
    CBSEENMA8003337

    What is the least number of planes that can enclose a solid? Name the simplest regular polyhedron and verify Euler’s formula for it.

    Solution
    At least 4 planes can form to enclose a solid. Tetrahedron is the simple polyhedron. Following figure represents a simplest solid, called tetrahedron.

     A tetrahedron has:
                  4 triangular faces, i.e. F = 4
                  4 vertices,             i.e. V = 4
                  6 edges,                i.e. E = 6
    Now, substituting the values of F, V and E in Euler's formula, i.e.
                                    F + V = E + 2
    we have
                                   4 + 4 = 6 + 2 
    rightwards double arrow                            8 = 8, which is true.
           Thus, Euler's formula is verified for a tetrahedron.
    Question 45
    CBSEENMA8003338

    Name the figure shown here.
    (i) How many faces does it have?
    (ii) How many vertices does it have?
    (iii) How many edges does it have?

    Solution

    Solution not provided.
    Ans. Cuboid;
    (i) 8
    (ii) 8
    (iii) 12
             

    Question 46
    CBSEENMA8003339

    Write the number of
    (i) faces
    (ii) edges
    (iii) vertices for a triangular prism.

    Solution

    Solution not provided.
    Ans. (i) 5
            (ii) 9
            (iii) 6
             

    Question 47
    CBSEENMA8003340

    Number of faces of a pyramid is 5. Find the number of its vertices when its edges are 8.

    Solution

    Solution not provided.
    Ans. 5
             

    Question 48
    CBSEENMA8003341
    Question 49
    CBSEENMA8003342

    What is a triangular pyramid? What is a pyramid called if its base is a square?

    Solution

    Solution not provided.
    Ans. Square pyramid.
             

    Question 50
    CBSEENMA8003343
    Question 51
    CBSEENMA8003344

    Draw the net of a triangular prism whose base is an equilateral triangle.

    Solution

    Solution not provided.
             

    Question 52
    CBSEENMA8003345

    Match the following figures:

    Solution

    Solution not provided.
    Ans. (a) - (iii);        (b) - (iii);   (c) - (i);   (d) - (iv)

    Question 55
    CBSEENMA8003348
    Question 56
    CBSEENMA8003349
    Question 57
    CBSEENMA8003350
    Question 58
    CBSEENMA8003351

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