Question

Consider sunlight incident on a slit of width 10⁴ A. The image seen through the slit shall ______.

Options

• be a fine sharp slit white in colour at the center.

• a bright slit white at the center diffusing to zero intensities at the edges.

• a bright slit white at the center diffusing to regions of different colours.

• only be a diffused slit white in colour.

Answer 1

Consider sunlight incident on a slit of width 10⁴ A. The image seen through the slit shall be a fine sharp slit white in colour at the center.

Explanation:

Diffraction of Light is the phenomenon of bending of light around the comers of an obstacle/aperture of the size of the wavelength of light.

(A) Size of the slit is very large compared to wavelength

(B) Size of the slit is comparable to wavelength

In figure (A), no diffraction phenomenon is observed as the size of slit is weary large compared to wavelength. But in figure(B), there will be diffraction of light as size of slit is compared to the wavelength of light incident.

Here in the question, it is given, width of the slit

b = 104 Å = 104 × 10^-10 m = 10^-6 m = 1 pm

The wavelength of (visible) sunlight varies from 4000 Å to 8000 Å.

Hence the width of slit is comparable to that of wavelength, hence diffraction occurs with maxima at centre. So, at the centre all colours appear, i.e., mixing of colours from white patch at the centre.