What is Double-Slit Interference and How to Calculate the Position of Bright Fringes?

How does a parallel beam of light from a He-Ne laser with a wavelength of 633 nm falling on two narrow slits create an interference pattern?

Understanding Double-Slit Interference

When a parallel beam of light from a He-Ne laser with a wavelength of 633 nm falls on two very narrow slits that are 0.070 mm apart, an interference pattern is observed. This pattern is a result of the phenomenon known as double-slit interference. In double-slit interference, light waves passing through the two slits interfere with each other, creating alternating regions of constructive and destructive interference. The interference pattern consists of bright fringes (where constructive interference occurs) and dark fringes (where destructive interference occurs).

Calculating the Position of Bright Fringes

To determine the position of the bright fringes, we can use the formula for the position of the bright fringe (m) on a screen placed at a distance (D) from the slits:

y = (mλD) / d

Where:
  • y is the distance from the central maximum to the mth bright fringe
  • λ is the wavelength of the light (633 nm in this case)
  • D is the distance from the slits to the screen
  • d is the distance between the two slits (0.070 mm in this case)
The interference pattern will have bright fringes spaced at regular intervals on the screen. By calculating the position of these fringes using the formula, you can determine the distance between them.

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