Phy103: Fundamentals of Physics III Lab
Instructor: Tony Zable
Part 1: Diffraction of Laser Light using a pin needle
1) Place a piece of tape over the on/off button of a laser pointer then place it on its side on the table top.
2) Aim the laser pointer toward a wall on the far side of the lab room.
3) Observe the pattern of the beam on the wall. Record your observations and sketch the beam pattern.
4) Place a pin needle (vertical orientation) about 5 to 8 cm in front of the laser pointer, directly in the path of the light beam (see Figure A).
5) Observe the pattern of the beam on the wall (make sure that the pin needle is directly in the light path). Record your observations and sketch the beam pattern.
6) Remove the pin needle and position it such that the head of the needle is directly in front of the beam path (see Figure B).
7) Observe the pattern of the beam on the wall (make sure that the head of the pin needle is directly in the light path). Record your observations and sketch the beam pattern.

Phy103: Fundamentals of Physics III Lab
Instructor: Tony Zable
8) How do the patterns in steps 5 and 7 compare?
Part 2: Single Slit Diffraction of Laser Light
1) Position 2 pieces of electrical tape so that their edges are parallel and roughly 0.5 mm apart.
2) Place the slit directly in the laser pointer’s light path such that you can observe the beam pattern on the wall on the far side of the lab room.
3) Observe the beam pattern on the wall. Record your observations and sketch the beam pattern.
4) Decrease the width of the slit by about half (~0.2 cm). An easy way to decrease the slit width is to use an additional piece of tape, placed so that it covers about ½ of the slit width.
5) Observe the pattern of the beam through the modified slit. Record your observations and sketch the beam pattern.
6) How does the pattern in step 5 compare to the pattern you observed in step 3.
Part 3: Diffraction of Laser Light through a pin hole
1) Using a pin needle, carefully poke a small round hole in a piece of electrical tape.
2) Place the piece of tape directly in front of the laser pointer’s light path such that the beam passes through the pin hole.
3) Observe the beam pattern on the wall. Record your observations and sketch the beam pattern.

Phy103: Fundamentals of Physics III Lab
Instructor: Tony Zable
Part 4: How does the wavelength of light affect the diffraction of photons?
To this point you have explored the phenomenon of light diffraction for a laser beam (i.e. a single color of light) and have observed how various obstructions can produce diffraction patterns. The question then begs, does the light itself affect diffraction? Since I am asking the question, the answer is probably an obvious, “yes”. So let’s explore this a little further.
1) Obtain a diffraction grating, meter stick, ring stand, spectrum power source and a mercury gas tube.
2) Set-up the gas tube and power source.
3) Attach a diffraction grating to a ring stand about 1 meter in front of the light source and adjust to about mid level of the light source. Note: the orientation of the grating should be parallel to the upright orientation of the light source.
4) Observe the light source through the diffraction grating. Record your observations:
5) Place a meter stick on top of the light source and determine the distance of each spectral line from the center of the light source. Be sure to measure the line on each side of the light source.
Line Color
Location of
Left Line
(measured from the center)
Location of Right
Line
(measured from the center)
Average Location of Line
Wavelength
(nm)
6) Calculate the average distance from the center and record this value in the above table.
7) For the mercury light source, there are 3 primary spectral lines, yellow (579 nm), green (546 nm) and violet (436 nm). Record these wavelengths in above table.
8) How does position of the line spectra vary with wavelength?
9) How does position of the line spectra vary with frequency?
10) How does position of the line spectra vary with photon energy?

Phy103: Fundamentals of Physics III Lab
Instructor: Tony Zable
Questions:
1) How does the pattern of light emitted from a laser change a small object is placed in its path?
2) How does the pattern of light emitted from a laser change when it passes through a small opening?
3) What is the relationship between the width of the slit and the resulting diffraction pattern?
4) How does the diffraction pattern as a light beam passes through a single slit compare to that produced when the beam passes through a small round hole.
5) Explain how wavelength affects the magnitude of diffraction?