Interference Fringes Shift Concepts

• Interference fringes shift when one of the slits is covered with a thin glass plate: This occurs because the glass plate introduces a phase difference between the light waves passing through the two slits, causing the fringes to shift.

• The shift is towards the side of the covered slit: This is because the light waves passing through the covered slit travel a longer distance than the waves passing through the uncovered slit, resulting in a phase difference that shifts the fringes towards the covered side.

• The amount of shift depends on the thickness of the glass plate and the wavelength of light: The thicker the glass plate, the greater the phase difference and the larger the shift. Similarly, the shorter the wavelength of light, the greater the phase difference and the larger the shift.

• The shift is due to the change in the optical path length of the light waves passing through the glass plate: The optical path length is the distance that light travels multiplied by the refractive index of the medium it is passing through. The glass plate has a higher refractive index than air, so the light waves passing through the glass plate travel a longer optical path length than those passing through the air, resulting in a phase difference.

• The shift can be used to measure the thickness of the glass plate or the wavelength of light: By measuring the amount of shift and knowing the refractive index of the glass plate, the thickness of the plate can be determined. Similarly, by knowing the thickness of the glass plate, the wavelength of light can be determined.