Light of wavelength strikes a photo-sensitive surface and electrons are ejected with kinetic energy E. If the kinetic energy is to be increased to 2E, the wavelength must be changed to
A
λ′=λ2
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B
λ′=2λ
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C
λ2<λ′<λ
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D
λ′>λ
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Solution
The correct option is Cλ2<λ′<λ E=hcλ−W0and2E=hcλ′−W0 ⇒λ′λ=E+W02E+W0⇒λ′=λ(1+W0/E2+W0/E) Since(1+W0/E)(2+W0/E)>12soλ′>λ2