Question

Irina finds an unlabeled box of fine needles, and wants to determine how thick they are. A standard ruler will not do the job, as each needle is less than a millimeter thick. So, to find the thickness, she uses a needle to poke a hole in a piece of brown construction paper. Then, she positions a 657 nm 657 nm laser pointer to shine through the hole and project a circular diffraction pattern on a wall 23.7 m 23.7 m away. She then uses her ruler to measure that the central bright circle is 16.2 cm 16.2 cm in diameter. What diameter does Irina calculate for the needle?

Answer 1

Step-by-step explanation:

y1 = 16.2/2 = 8.1 cm

d = 1.22 lambda D/y1

d = 1.22 x 657 x 10^-9 x 23.7/0.081

d = 2.35 x 10^-4 m = 234.52 um