Ultra-violet light of wavelength 200 nm from a source is incident on a metal surface. If the stopping potential is -2.5 V,
(a) calculate the work function of the metal, and
(b) How would the surface respond to a high intensity red light of wavelength 6328 ? produced by a laser?

K.E.max =hν -ϕϕ is work fucntionK.E.max = eVoeVo =hcλ -ϕ1.6×10-19(-2.5) =6.6×10-34×3×108200×10-9 m -ϕϕ =6.6×10-34×3×108200×10-9 m+1.6×10-19(2.5) ϕ = 0.099×10-17 +4×10-19= 9.9×10-19 +4×10-19ϕ =13.9 ×10-19 J = 8.68 eVThershold wavelengthλ =hcϕ =6.6×10-34×3×10813.9 ×10-19 =1.4244×10-7=1424 ×10-10 mAs wavelength of red light is greater than thershold wavelengththe surface will not respond to a high intensity red light of wavelength

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