Virtual Labs

Measurement of Wavelength of a Laser (He-Ne) Light using Single-Slit Diffraction

1. In a Fraunhofer diffraction experiment, what does the order (k) in the formula d sinθ = kλ refer to?

a: The number of diffracting slits used Explanation

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b: The colour of the light source Explanation

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c: The type of material used for the aperture Explanation

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d: The location of a particular dark fringe relative to the central maximum Explanation

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2. A single slit diffracts white light. Which colour deviates the most from the straight-through (central) direction?

a: Red — longer wavelengths diffract more Explanation

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b: Green Explanation

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c: Blue Explanation

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d: All colours deviate by the same amount Explanation

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3. Which parameter must be measured in the simulation to calculate the wavelength of the He–Ne laser in a single-slit diffraction setup?

a: Distance between two consecutive bright fringes Explanation

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b: Position of the central maximum only Explanation

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c: Angle of observation (θ) at the first-order minimum Explanation

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d: Total intensity of the diffraction pattern Explanation

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4. If the distance between the slit and the screen (D) is doubled in a single-slit diffraction experiment (keeping d and λ constant), the physical fringe width on the screen will:

a: Become half Explanation

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b: Become double Explanation

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c: Become four times Explanation

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d: Remain unchanged Explanation

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5. He–Ne laser light is used in diffraction experiments mainly because:

a: It generates a large amount of heat Explanation

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b: It produces monochromatic and coherent light Explanation

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c: It changes colour during propagation Explanation

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d: It produces a highly divergent beam Explanation

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6. In a single-slit diffraction experiment, d = 0.1 mm and the first-order minimum is observed at θ = 0.363°. What is the wavelength of the laser?

a: 400 nm Explanation

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b: 532 nm Explanation

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c: 633 nm Explanation

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d: 780 nm Explanation

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7. In the intensity formula for single-slit diffraction I = I₀(sinα/α)², what is the intensity at the centre of the central maximum (θ = 0)?

a: 0 Explanation

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b: I₀/2 Explanation

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c: I₀/π Explanation

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d: I₀ Explanation

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8. Which of the following correctly describes the secondary maxima in a single-slit diffraction pattern?

a: They are brighter than the central maximum Explanation

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b: They all have equal intensity Explanation

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c: Their intensity decreases with increasing order Explanation

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d: Their width is twice the width of the central maximum Explanation

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9. In a single-slit diffraction experiment, which combination produces the sharpest (narrowest) central maximum?

a: Wide slit and short wavelength Explanation

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b: Narrow slit and long wavelength Explanation

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c: Narrow slit and short wavelength Explanation

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d: Wide slit and long wavelength Explanation

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10. If the slit width in a single-slit diffraction experiment is made equal to the wavelength of light (d = λ), the first-order minimum will appear at:

a: θ = 30° Explanation

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b: θ = 45° Explanation

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c: θ = 90° Explanation

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d: No minimum will be observed on the screen Explanation

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