# expt 1 - 1 Experiment 1 Wave Nature of Light Interference...

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1 Experiment 1. Wave Nature of Light: Interference and Diffraction of Laser Light PHY 134 (Section 11)

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2 Purpose The experiment was done to help observe and establish the wave-like nature of light. Apparatus Two rulers, Magnetic bench, Straight edge/Opaque disks slide, Helium-neon laser, 48mm focal length lens, Slide with several narrow single slits, Slide with double slits, Diffraction grating slide, Hologram, and Calculator. Theory In the laboratory experiment, diffraction of light, a form of interference, is investigated using a laser. The light from a laser is collimated, monochromatic, and coherent. Which means that the beam does not diverge very much, the wavelength is constant, and all the oscillators in the beam are in phase with each other. The relationship between wavelength (λ), frequency (f), and speed of light (c) can be expressed c = fλ. Light travels with a constant speed within the same indices of refraction, and in air light travels with a speed of 3.0 * 10 8 m/s. Figure 1. Diagram of the narrow slit experiment
3 For the first two experiments, quantitative analysis is not required. But for narrow slit experiment, the formula λ = aw/2L is used, where λ is wavelength, a is the width of the slit, w is the width of the central peak, and L is the distance to screen (Fig 1). The formula is derived from a sinθ =λ, tanθ = w/2L, and using the right triangle. Since the angle θ is very small, sinθ and tanθ can be set equal to each other. Figure 2. Diagram of the double slit experiment In the double slit experiment, two slits are separated by a distance d, and two beams interfere with each other. When the two beams arrive at the screen in phase, bright spots can be observed, and it is called constructive interference. For this experiment, the condition is dsinθ = mλ, where m is the order of the bright band (Figure 2). Using the small angle approximation, λ = dy/mL can be derived. The Diffraction grating makes a very accurate wavelength measurement. Formulas

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expt 1 - 1 Experiment 1 Wave Nature of Light Interference...

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