Rules and procedures for TAs

Physical Optics 1st year physics laboratories University of Ottawa https://uottawa.brightspace.com/d2l/home INTRODUCTION Physical optics deals with light as a wave which can bend around obstacles (diffraction) and constructively or destructively interfere (interference). Visible light has a very short wavelength (~400 700 nm) therefore its wave-like properties can be difficult to observe. In todays experiment, you will examine various wave-like properties of light such as:

Diffraction from a single slit / double slit / grating Dispersion of light using a grating Diffraction around a spherical obstacle Attenuation of light using polarizers INTRODUCTION (cont.) Light waves being blocked by an obstacle can bend around it much like water or sound waves. If a narrow slit is placed in front of an incident wave, a new wave will spread out on the opposite side as if the slit were a point source of waves. DIFFRACTION PATTERN

The interference of light waves by diffraction through a single slit, double slit, or diffraction grating will cause a pattern of bright (constructive) and dark (destructive) spots when imaged on a screen. To best observe diffraction and interference, we use a monochromatic and coherent light source. If the size and spacing of the slits are known, we can calculate the wavelength of the light using some simple formulas. DIFFRACTION FROM A SINGLE SLIT For light passing through a single slit, Huygens Principle explains that any point

within the slit acts as a new source of emitted waves. The equation for the angle to the minima in the interference pattern is given by: Using the small angle approximation and trigonometry, we can solve for the slit width: INTERFERENCE FROM A DOUBLE SLIT An incident wave passing through a double-slit will spread out on the opposite side as two new sources of emitted waves, ready to interact with each other. The equation for the angle to the maxima in the interference pattern is given by:

Using the small angle approximation and trigonometry, we can solve for the slit POLARIZATION A polarizer will only allow light which is vibrating in a particular plane or axis of polarization to pass through it. The portion of unpolarized light (vibrating in all planes) that passes through the polarizer becomes polarized in this axis. If polarized light is sent through a 2nd polarizer, the intensity of light transmitted is given by Malus Law: where is the intensity of light passing through the first filter and is the angle between the axes of the two polarizers.

SETUP: DIFFRACTION FROM A SLIT diffraction slit assembly screen lens diffraction gratings laser SETUP: DISPERSION FROM A GRATING Laser (turned off)

screen gratings lens white light SETUP: SPECTRUM OF A MERCURY LAMP (1 per class) screen lens & gratings

mercury lamp SETUP: DIFFRACTION AROUND AN OBSTACLE 1 PER CLASS screen bead lens laser SETUP: POLARIZATION OF LIGHT

light sensor white light polarizer 1 polarizer 2 CLEAN UP Turn off the computer and dont forget to take your USB key. Make sure the laser and the white light source are turned off. Leave the following components on the optical track in that order: light source polarizers (2) light sensor screen diffraction slit assembly laser. Leave the lens nearby the bench.

Please recycle scrap paper and throw away any garbage. Please leave your station as clean as you can. Push back the monitor, keyboard, and mouse. Please push your chair back under the table. DUE DATE The report is due at the end of the lab session. You are about to complete your last physics lab for this semester! Equipment information: the laser Your setup includes a red or green

laser. Red laser: wavelength of 636 nm. Green laser: wavelength of 532 nm. Laser Safety This is a class 2 laser product. Do not stare directly into the laser beam or its reflection. Maximum output is < 1 mW. A class 2 laser is generally considered safe as the blink reflex will limit exposure to short time periods. Most laser pointers are in this class. Direct exposure on the eye by a beam of laser light should always be avoided with any laser, no matter how low the power.

Equipment information: the slit assembly Single slits 0.02 mm 0.04 mm 0.08 mm 0.16 mm Variable slits Wedge: 0.02 0.2 mm wide

Double Slit: 0.04 mm wide, spacing 0.125 0.75 mm Double slits 0.04 mm wide, 0.25 mm apart 0.04 mm wide, 0.5 mm apart 0.08 mm wide, 0.25 mm apart 0.08 mm wide, 0.5 mm apart Variable double slit Same as variable slits

Multiple slits Comparisons 4 sets: 4 pairs of single/double slits: 2, 3, 4, 5 slits 0.04 mm single + 0.04/0.25 mm double, 0.04 mm wide at 0.25 mm apart

doubles 0.04/0.25mm + 0.04/0.50 mm, doubles 0.04/0.25 mm + 0.08/0.25 mm, double 0.04/0.25 mm + triple, 0.04/0.25 mm

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