10th Class Science Sources of Energy Question Bank Sources of Energy

  • question_answer
    When a cathode ray tube is operated at 2912 volt, then velocity of electrons is \[\text{3}.\text{2 }\times \text{ 1}{{0}^{7}}\] m/s. The velocity of cathode ray, if the tube is operated at 5824 volt, will be

    A) \[\text{4}.\text{48 }\times \text{ 1}{{0}^{\text{6}}}\text{ m}/\text{sec}\]

    B)        \[\text{4}.\text{48 }\times \text{ 1}{{0}^{\text{7}}}\text{ m}/\text{sec}\]  

    C) \[\text{8}.\text{44 }\times \text{ 1}{{0}^{\text{6}}}\text{ m}/\text{sec}\]

    D)         \[\text{8}.\text{88 }\times \text{ 1}{{0}^{\text{7}}}\text{ m}/\text{sec}\]

    Correct Answer: B

    Solution :

                    \[eV=\frac{1}{2}m{{v}^{2}}\] \[\Rightarrow \]               \[v=\sqrt{\frac{2eV}{m}}\] \[\Rightarrow \]               \[\frac{v}{\sqrt{V}}=\sqrt{\frac{2e}{m}}=\]constant \[\therefore \]  \[\frac{{{v}_{1}}}{\sqrt{{{V}_{1}}}}=\frac{{{v}_{2}}}{\sqrt{{{V}_{2}}}}\] \[\Rightarrow \]               \[{{v}_{2}}={{v}_{1}}\sqrt{\frac{{{V}_{2}}}{{{V}_{1}}}}\]                     \[=3\times 2\times {{10}^{7}}\sqrt{\frac{5824}{2912}}\]                     \[\mathbf{=4}\mathbf{.48\times 1}{{\mathbf{0}}^{\mathbf{7}}}\mathbf{m/sec}\]


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