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$基于速度选择器的质谱仪,离开速度选择器的速度是相同的,因为速度选择器只筛选速度,不筛选\cfrac{q}{m}$
$r=\cfrac{mv}{qB},因而半径只以比荷\cfrac{q}{m}有关,\cfrac{q}{m}越大,r越小$
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$1.qvB=q\cfrac{U}{d}\Rightarrow v=\cfrac{U}{dB_1}$
$2.R=\cfrac{mv}{qB_2}=\cfrac{m}{qB_2}\cfrac{U}{dB_1}=\cfrac{mU}{qdB_1B_2}$
$3.同位素的电荷相等,质量不同 R=\cfrac{mv}{qB}\Rightarrow \cfrac{m_1}{m_2}=\cfrac{R_1}{R_2}=2:3$
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速度选择器只选择速度,没法判断其电量质量和电性。电性由偏转磁场来判定。D
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C
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D
基于加速电场的质谱仪

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若粒子的电量相同，则初动能相同
$\cfrac{1}{2}mv^2=qU\Rightarrow v=\sqrt{\cfrac{2qU}{m}},r=\cfrac{mv}{qB}=\cfrac{1}{B}\sqrt{\cfrac{2Um}{q}},与比荷的开平方成反比\sqrt{\cfrac{m}{q}}$
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A
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$1.V=\sqrt{\cfrac{2qU}{m}};2.B=\cfrac{2}{x}\sqrt{\cfrac{2mU}{q}}.3.\cfrac{\sqrt{3}}{2}x=\cfrac{m_bv}{qB}=\cfrac{1}{B}\sqrt{\cfrac{2m_bU}{q}}\Rightarrow$
$\cfrac{3}{4}x^2=\cfrac{1}{B^2}\cfrac{2m_bU}{q}\Rightarrow m_b=\cfrac{3x^2B^2q}{8U}=\cfrac{3x^2q}{8U}\cdot\cfrac{4}{x^2}\cdot\cfrac{2mU}{q}=3m$