Lab 10: Wave optics Only 2 more labs to go!! Light is an electromagnetic wave. Because of the wave nature of light it interacts differently than you might expect. Consider the following situation: light rays double slits screen double slits Wave front from light light source

screendouble slits intensity maxima d R1R1 R2R2 The maximas in intensity occur when the difference in path (from the two slits) is equal to an integral number of wavelengths. In other words, when: It can be shown from trigonometry that,  D So then we will have points of maximums when: Notice that for small angles,  < 5 o, sin  = tan , and for this situation tan  is: Where d, is the slit separation,  is the angle between the maxima and the optical axis, n is the order of intensity (i.e. n = 1, 2 3,..etc.), and is the wavelength of light. y where, y is the distance the maxima is from the central maxima, and D is the distance between the screen and the grating. central maxima

So our equation becomes: Today, you are going to measure the distance spots occur from the central maxima. From this you will be ask to calculate the slit separation and the wavelength. Let’s look at this example: White light is incident upon a regular array of slits. An interference pattern is observed on a screen, a distance of 8 meters from the slits. It is noted that the second order yellow ( = 550 nm) is at a horizontal distance of 10 cm from the center. What will be the location of the first order yellow? Unfortunately, we don’t have the slit separation so we need to solve for d, first. Remember that the second order spot is found 10cm away from the center, so we can use this information to calculate d: Using this we can solve for y and we get: y = 0.05 m