18. A stopping potential of 4.2 V is needed for radiation whose wavelength is 200 nm. The work function in eV of the material is (A) 4 (B) 3 (C) 5 (D) 6 (E) 2

6. Two far apart charged metal spheres of radius R₁ and R₂ are connected by a long wire in electrostatic equilibrium. The electric potentials and the surface charge densities on them are V₁, V₂ and σ₁, σ₂, respectively. Choose the correct statement. (A) V₁ ＞ V₂, σ₁ ＞ σ₂ (B) V₁ ＜ V₂, σ₁ ＜ σ₂ (C) (D) V₁ = V₂, R₁σ₁ = R₂σ₂ (E) R₁V₁ = R₂V₂, σ₁ = σ₂

18. A stopping potential of 4.2 V is needed for radiation whose wavelength is 200 nm. The work function in eV of the material is
(A) 4
(B) 3
(C) 5
(D) 6
(E) 2

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