用频率为ν的光照射某金属表面，恰好发生光电效应。若改用频率为2ν的光照射同种金属，则逸出的光电子最大初动能为多少？（已知普朗克常量为h）
Show the answer and explanation
Correct answer
A. hν
Principle or equation
爱因斯坦光电效应方程：Eₖmax = hν - W₀。恰好发生光电效应时，hν = W₀。
Why this answer is correct
恰好发生光电效应时，最大初动能为零，故逸出功W₀ = hν。改用频率2ν的光时，Eₖmax = h(2ν) - hν = hν。
Example
若逸出功为2 eV，光子能量为5 eV，则最大初动能为3 eV。
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