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A metallic surface is illuminated with radiation of wavelength λ, the stopping potential is V 0 . If the same surface is il luminated with radiation of wavelength 2λ, the stopping potential becomes 4 V 0 . The threshold wavelength for this metallic surface will be :

1. 3λ
2. 4λ
3.  2 3
4. 4 

Correct answer: 3λ

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