11th Class Physics Physical World / भौतिक जगत Question Bank 11th CBSE Physics Mathematical Tools, Units & Dimensions

  • question_answer
    If p represents radian pressure, c represents the speed of light and q represents the radiation energy, per unit area per unit time, then calculate non-zero integers such that \[{{p}^{x}}{{q}^{y}}{{c}^{z}}\] is dimensionless.

    Answer:

                    Here,                                                      \[\text{p }=\frac{ML{{T}^{-2}}}{{{L}^{2}}}=[M{{L}^{-1}}{{T}^{-2}}]\]                                                               \[\text{c}=\left[ \text{L}{{\text{T}}^{-\text{1}}} \right]\]                  \[\text{q }=\frac{energy}{area\times time}=\frac{M{{L}^{2}}{{T}^{-2}}}{{{L}^{2}}T}=[M{{T}^{-3}}]\]                                                                                                       \[\therefore\]   \[{{\text{p}}^{\text{x}}}{{\text{q}}^{\text{y}}}{{\text{c}}^{\text{z}}}=\text{ }{{\left( \text{M}{{\text{L}}^{-\text{1}}}{{\text{T}}^{-\text{2}}} \right)}^{\text{x}}}{{\left( \text{M}{{\text{T}}^{-\text{3}}} \right)}^{\text{y}}}{{\left( \text{L}{{\text{T}}^{-\text{1}}} \right)}^{\text{z}}}=\text{ }{{\text{M}}^{\text{x }+\text{ y}}}{{\text{L}}^{-\text{x }+\text{ z}}}{{\text{T}}^{-\text{2x}}}^{-\text{3y}-\text{z}}\] It will be dimensionless, if                                         \[\text{x}+\text{y}=0\]                                                                                                                                                                                                  \[\therefore\]                                                                                                               \[x=-y\]                                                                                             \[\text{x }+\text{ z }=0\] and                                                                   \[\text{x}=\text{z}\text{2x}\text{3y}-\text{z}=0\] These equations have infinite solutions. One of the solutions is x = 1,y = -1 and z = 1, so that                                                                                        \[{{p}^{x}}{{q}^{y}}{{c}^{z}}\] isdimensionless.


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