DETERMINING WAVELENGTH FROM INTERFERENCE Activity 1-1 In this activity, you will study the interference of two circular water waves and determine the wavelength from the interference pattern. . Attach the point-source generators on the black, plastic bar on the ripple generator. The point-source generators are plastic pegs that snap onto the bar. Place two pegs about 5 cm apart at the center of the bar by snapping the pegs onto the bar. Using the right hand red knob on the generator, lower the bar such that the tips of the pegs touch the surface of the water. Using the right hand red knob on the generator, lower the bar such that the tips of the pegs touch the surface of the water. Question 1-1: Now turn on the ripple generator. Do you see a wave pattern like that shown in t Introduction? If not, call over your instructor. Yes Let's now determine the wavelength by making measurements on the first and second nodal lines n=1 and n=2. Refer to Figure 10-4 and Equations (2) and (3) of the Introduction. We will need to know x and L to determine Sino = ( n - 1/2 ) ( xd ) 0 from Equation (3), and then d and n to determine 1 from Equation (2). tano= x L . Position the whiteboard under the ripple tank so that the whole wave pattern is displayed on the whiteboard. Draw a line on the whiteboard parallel to the vibrating bar on the ripple generator to indicate the location of the "viewing screen". Measure L on the whiteboard and record this value in Table 10-1. Measuring x directly would require locating the midpoint of the central maximum. It is easier to measure 2x , the distance between corresponding points on the n -th nodal line on each side. Measure 2x forn = 1 and n = 2 on the white board and record these values in Table 10-1. Calculate x from 2x and enter these values into Table 10-1. . Note that L and 2x you measure projected on the white board are different from their actual lengths on the surface of the water. However, since all we need is the ratio x /L to determine 0, there is no need to convert them to actual lengths. (Angles do not change under scaling!) Calculate tano, sine , and then determine 1 . Enter these values into Table 10-1. Lab 10: Diffraction and Interference 10-8Repeat your measurement for n = 1 with a new value of d around 10 cm. Add your new measurements and calculations to Table 10-1. tang : 4/L sino: (4- 1 12 ) ( No ) Table 10-1 n d (cm) L (cm) 2x (cm) x (cm) tan 0 sin 8 a (cm) actual projected projected projected actual 5 24.8 9.4 4.7 0. 1895 10.73 0, 18 62 1. 8 6 1 2 5 24.4 27.4 11.2 0. 4516 24. 30 0. 4/15 1.372 1 10 11. 1 1.9: 0.95 10.08559 4.89 /0585 24 1. 705 Question 1-2: Should the wavelength be the same for all three trials? Explain. Question 1-3: Discuss potential sources of error in this experiment Lab 10: Diffraction and Interference 10-9