A healthy, normal, adult\'s eye has a far point at infinity and a near point of

Question

A healthy, normal, adult's eye has a far point at infinity and a near point of 25 cm. If the lens/retina distance is exactly 2.0 cm, what range of focusing power can be attributed to the lens/cornea combination? When ultraviolet light of wavelength 100 nm. Shines on a particular metal in vacuum the maximum kinetic energy of ejected photoelectrons is 10.0 eV. Longer wavelengths produce less energetic electrons. Above what threshold wavelength would no photoelectrons be detected? Bohr's theory of hydrogen-like atoms predicts energy levels En = -13.6 Z^2/n^2 eV where Z is the atomic number. What wavelength would be produced by the n=3 to n=2 transition in Be, for which Z=4. Fundamental Constants e=1.6 times 10^-19C h=6.6 times 10^34J c=3.0 times 10^8 m/s k=9.0 times 10^9Nm^2C^-2

Explanation / Answer

for far point

object distance s = infinity

1/inifnity + 1/2 = 1/f

f = 2 cm

power = 1/f(in m) =1/0.02 = 100/2 = 50 D

for near point

1/25 + 1/2 = 1/f

f = 1.85 cm

power = 100/1.85 = 54 D

from 50 D to 54 D

++++++++++++

E = Wo + KE

Wo = E - KE

h*c/Lo = hc/L - K

(6.626*10^-34*3*10^8)/Lo = (6.626*10^-34*3*10^8)/(100*10^-9) - (10*1.6*10^-19)

Lo = 512.5 nm <<---answer

+++++++++++

E3 = 13.6*4^2/3^2 = -24.18 eV

E2 = 13.6*4^2/2^2 = -54.4 eV

E3 - E2 = 30.22

E3 - E2 = hc/L

30.22*1.6*10^-19 = (6.626*10^-34*3*10^8)/L

L = 41.1 nm

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