when light of 3000 armstrong is incident on sodium cathode ,the stopping potential is 1.85V and when light of 4000 armstrong is incident then the stopping potential becomes 0.82v.calculate :plank's constant ,work function of sodium,threshold wavelength for sodium.

Einstein Photoelectric equation:E=W+KEhcλ=hcλ0+KECase I:hc3000×10-10=hcλ0+1.85 eVhc3000×10-10=hcλ0+1.85 ×1.6×10-19 Jhc3000×10-10=hcλ0+2.96×10-19 ...... (1)Case II:hc4000×10-10=hcλ0+0.82 eVhc4000×10-10=hcλ0+0.82 ×1.6×10-19 Jhc4000×10-10=hcλ0+1.312×10-19 ...... (2)(1) - (2):hc13000×10-10-14000×10-10=1.648×10-19hc8.33×105=1.648×10-19h=1.648×10-198.33×105×3×108 =6.6×10-34 m2kg/sWork function:W=E-KE =hc3000×10-10-2.96×10-19 =6.6×10-34×3×1083000×10-10-2.96×10-19 =3.632×10-19 JThreshold wavelength:λo=hcW =6.6×10-34×3×1083.632×10-19 =5.452×10-10 m =5452 A

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