Light of wavelength 650 nm is incident normally upon a glass plate. The glass pl

Question

Light of wavelength 650 nm is incident normally upon a glass plate. The glass plate rests on top of a second plate so that they touch at one end and are separated by 0.0325 mm at the other end as shown in the figure. Which range of values contains the horizontal separation between adjacent bright fringes? (120 mm across)

2. In two separate double slit experiments, an interference pattern is observed on a screen. In the first experiment, violet light (? = 708 nm) is used and a second-order bright fringe occurs at the same location as a third-order dark fringe in the second experiment. Determine the wavelength of the light used in the second experiment.

Explanation / Answer

Apply 2nt = (m + .5)(wavelength)

2(1)(3.25 X 10-5) = (m+.5)(650 X 10-9)

m = 100

120/100 = 1.2 mm (Choice B - 1.2 is between 1.1 and 1.4)

Number 2)

For a double slit, the formula that applies is

y/L = m(wavelength)/d for brights and y/L = (m+.5)wavelength/d for darks

In this case, y L and d are constant

m(wavelength) = (m+.5)wavelength

2(708) = (2.5)(wavelength)

wavelength = 566.4 nm

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