JEE Physics 2026 Question with Solution

Given: Single slit diffraction.

Find: Which statements are true and which option matches the solution working.

For single slit diffraction, the angular width of the central maximum is

$$\theta = \frac{2\lambda}{a}$$

where $\lambda$ is the wavelength and $a$ is the slit width.

From this relation, the width of the central maximum is directly proportional to $\lambda$ and inversely proportional to $a$.

Statement A: If slit width is constant and wavelength increases, then width increases. So A is correct.

Statement B: If wavelength decreases while slit width is constant, the width decreases. So B is incorrect.

Statement C: If slit width decreases at constant wavelength, then the width increases. So C is correct.

Statement D: If slit width increases at constant wavelength, the width decreases. So D is incorrect.

Statement E: Brightness of the central maximum does not increase merely because wavelength decreases at constant slit width. So E is incorrect.

Thus, the correct statements are A and C.

However, the listed options do not contain A and C. The solution itself inconsistently states "The Correct Option is C" and later shows "Final Answer: A, D only". Since the worked analysis clearly supports A and C, the most defensible mapped answer from the source is option C, following the explicit solution-page declaration.

Therefore, the recorded answer is C.

Given:

• Central maximum width in single slit diffraction depends on wavelength and slit width.

Find: Truth values of statements A to E.

Use

$$\theta = \frac{2\lambda}{a}$$

1. If $\lambda$ increases and $a$ is constant, then $\theta$ increases. So A is true.
2. If $\lambda$ decreases and $a$ is constant, then $\theta$ decreases. So B is false.
3. If $a$ decreases and $\lambda$ is constant, then $\theta$ increases. So C is true.
4. If $a$ increases and $\lambda$ is constant, then $\theta$ decreases. So D is false.
5. The statement about brightness does not follow from $\theta = \frac{2\lambda}{a}$, and the solution marks it false. So E is false.

Hence, the physically correct combination is A and C. Since no option matches this, the source contains an option mismatch. The extracted answer follows the solution-page option label declaration and is C.