JEE Main & Advanced Physics Photo Electric Effect, X- Rays & Matter Waves Question Bank Cathode Rays and Positive Rays

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    While doing his experiment, Millikan one day observed the following charges on a single drop            (i)   \[6.563\times {{10}^{-19}}C\] (ii)  \[8.204\times {{10}^{-19}}C\]            (iii)  \[11.50\times {{10}^{-19}}C\] (iv)  \[13.13\times {{10}^{-19}}C\]            (v)  \[16.48\times {{10}^{-19}}C\] (vi)  \[18.09\times {{10}^{-19}}C\]    From this data the value of the elementary charge (e) was found to be                                        [MP PMT 1993]

    A)            \[1.641\times {{10}^{-19}}C\]                                           

    B)            \[1.630\times {{10}^{-19}}C\]

    C)            \[1.648\times {{10}^{-19}}C\]                                           

    D)            \[1.602\times {{10}^{-19}}C\]

    Correct Answer: A

    Solution :

                       Any charge in the universe is given by \[q=ne\Rightarrow e=\frac{q}{n}\] (where n is an integer)           \[{{q}_{1}}:{{q}_{2}}:{{q}_{3}}:{{q}_{4}}:{{q}_{5}}:{{q}_{6}}::{{n}_{1}}:{{n}_{2}}:{{n}_{3}}:{{n}_{4}}:{{n}_{5}}:{{n}_{6}}\] \[6.563:8.204:11.5:13.13:16.48:18.09\]\[::{{n}_{1}}:{{n}_{2}}:{{n}_{3}}:{{n}_{4}}:{{n}_{5}}:{{n}_{6}}\] Divide by 6.563 \[1:1.25:1.75:2.0:2.5:2.75\]\[::{{n}_{1}}:{{n}_{2}}:{{n}_{3}}:{{n}_{4}}:{{n}_{5}}:{{n}_{6}}\] Multiplied by 4 \[4:5:7:8:10:11\]\[::{{n}_{1}}:{{n}_{2}}:{{n}_{3}}:{{n}_{4}}:{{n}_{5}}:{{n}_{6}}\] \[e=\frac{{{q}_{1}}+{{q}_{2}}+{{q}_{3}}+{{q}_{4}}+{{q}_{5}}+{{q}_{6}}}{{{n}_{1}}+{{n}_{2}}+{{n}_{3}}+{{n}_{4}}+{{n}_{5}}+{{n}_{6}}}=\frac{73.967\times {{10}^{-19}}}{45}\] \[=1.641\times {{10}^{-19}}C\] (Note : If you take 45.0743 in place of 45, you will get the exact value)


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