### Interference and Diffraction Pre-lab Assignment

Print this page, record your answers on it, and show it to your lab TF at the start of your lab session.

In this experiment you will use a laser and a set of narrow slits to investigate interference and diffraction. Waves exhibit interference and/or diffraction when they encounter openings and/or obstacles that are comparable in size to the wavelength.

The simulation above should help you answer the following questions.
In the top window of the simulation you will see a magnified view of the single or double slit. In the bottom window of the simulation you will see the pattern of light and dark fringes on a screen some distance from the slit(s).

1. A laser is shone through a double slit, two narrow openings placed close together. An interference pattern of bright and dark fringes is observed on a screen some distance from the double slit.

(a) If the separation between the openings in the double slit is increased, what happens to the distance between the fringes on the screen? That distance ...

 increases decreases stays the same

(b) If the distance between the double slit and the screen is increased, what happens to the distance between the fringes on the screen? That distance ...

 increases decreases stays the same

(c) If the wavelength of the laser light is increased, what happens to the distance between the fringes on the screen? That distance ...

 increases decreases stays the same

(d) If the double slit is turned into a triple slit by adding a third narrow opening halfway between the original two openings in the double slit, what happens to the distance between the fringes on the screen? That distance ...

 increases decreases stays the same

(e) If the entire apparatus is immersed in water, what happens to the distance between the fringes on the screen? That distance ...

 increases decreases stays the same

2. Briefly justify your answer to part (e) above.