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The kinetic energy of emitted electron is E when the light incident on the metal has wavelength λ. To double the kinetic energy, the incident light must have wavelength :

1. hc – E hc λ
2. hc E hc + λ λ
3. hc E hc + λ λ
4. hc – E hc λ λ

Correct answer: hc E hc + λ λ

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