NEET 2016 Phase 1 · PhysicsStopping pot.Previous Year Question
When a metallic surface is illuminated with radiation of wavelength λ, the stopping potential is V. If the same surface is illuminated with radiation of wavelength 2λ, the stopping potential is V/4. The threshold wavelength for the metallic surface is:
Answer: (D) 3λ. Answer: (d) 3λ Solution: eV = hc/λ − W ...(i) e(V/4) = hc/2λ − W ...(ii) From (i): combine ⇒ hc/λ − W = 4(hc/2λ − W) ⇒ 3W = hc/λ ⇒ W = hc/3λ.
- A.4λ
- B.5λ
- C.(5/2)λ
- D.3λ✓
Correct Answer
(D) 3λ
Solution & Explanation
Answer: (d) 3λ Solution: eV = hc/λ − W ...(i) e(V/4) = hc/2λ − W ...(ii) From (i): combine ⇒ hc/λ − W = 4(hc/2λ − W) ⇒ 3W = hc/λ ⇒ W = hc/3λ. Threshold: hc/λ₀ = W = hc/3λ ⇒ λ₀ = 3λ.
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