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An electron beam accelerated from rest through a potential difference of `5000 V`in vacuum is allowed to impinge on a surface normaly. The incident current is `muA` and if the electrons come to rest on striking the surface the force on it is:A. `1.1924 xx 10^(-8) N`B. `2.1 xx 10^(-8) N`C. `1.6 xx 10^(-8)N`D. `1.6 xx 10^(-6) N` |
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Answer» Correct Answer - A Energy `=(1)/(2)mv^(2) = 5000eV` `=5000 xx 1.6 xx 10^(-19)` joule `mv = sqrt(2xx5000 xx (16 xx 10^(-19)m))` `= 4 xx 10^(-8) xx sqrt(m)` Number of electron striking per second `=n = (q)/(e) = (It)/(e) = (50xx10^(-6)xx1)/(1.6 xx 10^(-19))` `= 31.25 xx 10^(13)` Force `=` change of momentum per second `=n(mv) = 31.25 xx 10^(13) xx 4xx10^(-8) sqrt(m)` `= 125 xx 10^(5) sqrt(9.1 xx 10^(-31))` `= 1.1924 xx 10^(-8)` newton |
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