Dual Nature of Radiation and Matter - Result Question 55

59. In a photo-emissive cell, with exciting wavelength λ, the fastest electron has speed v. If the exciting wavelength is changed to 3λ4, the speed of the fastest emitted electron will be

[1998]

(a) (3/4)1/2v

(b) (4/3)1/2v

(c) less than (4/3)1/2v

(d) greater than (4/3)1/2v

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Answer:

Correct Answer: 59. (d)

Solution:

(d) 12mv2=hcλW0 or hcλ=12mv2+W0 and

12mv12=hc(3λ/4)W0=43(12mv2+W0)W0

So, v1 is greater than v(43)1/2.



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