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Question

Physics Question on Ray optics and optical instruments

For what distance is ray optics a good approximation when the aperture is 4 mm4 \,mm wide and the wavelength is 500 nm500 \,nm?

A

32 m

B

64 m

C

16 m

D

8 m

Answer

32 m

Explanation

Solution

For ZFZ_F distance ray optics is a good approximation.
ZF=a2λZ_F=\frac{a^2}{\lambda}
Here, a=4×10−3m,λ=5×10−7ma = 4 \times 10^{-3}m, \lambda = 5 \times 10^{-7} m
∴Zf=16×10−65×10−7=32 m\therefore Z_f=\frac{16 \times10^{-6} }{5 \times10^{-7}}=32\, m