Question

Assertion $\left(\text{A}\right)$ : We cannot observe the diffraction pattern from a wide slit illuminated by monochromatic light.

Reason $\left(\text{R}\right)$ : In diffraction pattern all the bright bands are not of the same intensity.

• A. $\text{A}$ is false and $\text{R}$ is true.
• B. Both $\text{A}$ and $\text{R}$ are true and $\text{R}$ is the correct explanation of $\text{A}$.
• C. Both $\text{A}$ and $\text{R}$ are true and $\text{R}$ is not the correct explanation of $\text{A}$.
• D. $\text{A}$ is true and $\text{R}$ is false.

Answer 1

The correct option is C Both $\text{A}$ and $\text{R}$ are true and $\text{R}$ is not the correct explanation of $\text{A}$.

Diffraction is the bending of light from the edges of the obstacle when the size of the obstacle is comparable with the wavelength of light. i.e $a\approx \lambda$

But when a wide slit is illuminated by monochromatic light, diffraction will not occur because the size of the slit is much larger than the wavelength.

So, Assertion $\left(\text{A}\right)$ is true.

In diffraction the intensity of central bright fringe is maximum and the intensity of other bright fringes keeps on decreasing as we move further away from central bright fringe.

So, Reason $\left(\text{R}\right)$ is also true but $\text{R}$ is not the correct explanation of $\text{A}$.

$\therefore$ option $\left(\text{B}\right)$ is correct.