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How far from grains of red sand must you be to position yourself just at the limit of resolving the grains if your pupil diameter is 1.5mm, the grains are spherical with radius50μm , and the light from the grains has wavelength 650nm? (a) If the grains were blue and the light from them had wavelength 400nm, would the answer to (b) be larger or smaller?

Short Answer

Expert verified
  1. The distance between the grains and the eye is19.0cm .
  2. Length L will be larger

Step by step solution

01

Introduction

Wavelength is the distance between identical points (adjacent crests) in the adjacent cycles of a waveform signal propagated in space or along a wire.

02

Calculation

The pupil’s diameter'd'=1.55mm

The radius of sphereR=50 μm and wavelength 'λ'=650mm

Since θR=1.22λd=θi

d=1.22×650×10-9m1.5×10-3mθR=5.286×10-4 rad

Diameter of the sphere is

D=2R=250μm=100μm

03

(a) Determine the distance between grains and the eye

The distance between the grains and the eye is

\begingatheredL=Dd1.22λ=DθR=100×10-4m5.2867×10-4rad=18.9cmL=19.0cm

Hence, the distance is 19.0cm.

04

(b) Determine the wavelength is larger & smaller

If wavelength λ=400mm

Since L=Dd1.22λ

Lα1λ

Since λ=400nm is smaller than 650nm,

Hence, length L will be larger larger.

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