The human eye has an approximate angular resolution of $\theta=5.8 \times 10^{-4} \mathrm{rad}$ and typical photo printer prints a minimum of 300 dip (dots per inch, 1 inch $=2.54 \mathrm{~cm}$ ). At what minimal distance $d$ should a printed page be held so that one does not see the individual dots?

• A

  $20.32 \mathrm{~cm}$
• B

  $29.50 \mathrm{~cm}$
• Correct answer
  C

  $14.59 \mathrm{~cm}$
• D

  $6.85 \mathrm{~cm}$

Solution

$\theta=\frac{x}{d}$ $5.8 \times 10^{-4}=\frac{2.54}{300} \times \frac{1}{d}$ $d=14.59 \mathrm{~cm}$

Hence, the correct answer is option: 'C'.