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的光照射同一金属，则逸出的光电子的最大初动能变为多少？（已知普朗克常量为h）
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Correct answer
B. hν
Principle or equation
爱因斯坦光电效应方程：Ek = hν - W0，其中W0为逸出功。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0，所以逸出功W0 = hν。改用频率2ν时，Ek = h(2ν) - W0 = 2hν - hν = hν。
Example
若ν=5×10^14 Hz，则W0= hν，用2ν照射时Ek=hν。
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