Statement-1: In YDSE, if a thin film is indroduced in front of the upper slit then the fringe pattern shifts in the downward direction.
Statement-2: in YDSE if the slit widths are unequal the minima will be completely dark.

Options

A. Statement-1 is true, statement-2 is true: Statement-2 is a correct explanation for statement-1
B. Statement-2 is true, statement-2 is true: statement-2 is not a correct explanation for statement-1
C. Statement-1 is true, Statement-2 is false.
D. Statement-1 is false, Statement-2 is true.

Answer

To analyze the given statements in the context of Young's Double Slit Experiment (YDSE), we will evaluate each statement step by step.

### Step 1: Evaluate Statement 1
**Statement 1:** In YDSE, if a thin film is introduced in front of the upper slit, then the fringe pattern shifts in the downward direction.

**Analysis:**
1. In YDSE, when light passes through two slits, it creates an interference pattern on the screen due to the superposition of light waves from both slits.
2. If a thin film is placed in front of the upper slit, the light traveling through that slit will experience a change in optical path length due to the film.
3. The introduction of the thin film increases the optical path length for the light coming from the upper slit. This results in a phase shift.
4. To compensate for this additional path length, the central maximum (bright fringe) will shift upward on the screen, leading to an overall upward shift of the fringe pattern.

**Conclusion for Statement 1:** The statement is incorrect. The fringe pattern shifts upward, not downward.

### Step 2: Evaluate Statement 2
**Statement 2:** In YDSE, if the slit widths are unequal, the minima will be completely dark.

**Analysis:**
1. In YDSE, the intensity of the interference pattern depends on the amplitudes of the light waves coming from each slit.
2. If the slit widths are unequal, the amplitudes of the light waves from each slit will also be unequal.
3. The condition for destructive interference (minima) occurs when the path difference between the two waves is an odd multiple of half the wavelength.
4. However, due to the unequal amplitudes, even at the minima, there will be some residual intensity because the waves do not completely cancel each other out.
5. Therefore, the minima will not be completely dark; they will be dimmer than the maxima but will still have some intensity.

**Conclusion for Statement 2:** The statement is incorrect. The minima will not be completely dark.

### Final Conclusion:
Both statements are incorrect.