In Young's double slit experiment:

Options

A. The interference pattern has a number of equally spaced bright and dark bands
B. The interference pattern has a central bright maximum which is twice as wide as other maximum
C. Intensity of all bright bands is same
D. Both (1) & (3)

Answer

To solve the question regarding Young's double slit experiment, we will analyze each of the options provided and determine their validity based on the principles of interference and intensity distribution.

### Step-by-Step Solution:

1. **Understanding the Setup**:
In Young's double slit experiment, two coherent light sources (slits S1 and S2) produce an interference pattern on a screen. The waves from these slits overlap and create regions of constructive and destructive interference.

**Hint**: Remember that coherent sources are essential for producing a stable interference pattern.

2. **Analyzing Option 1**:
The first option states that the interference pattern has a number of equally spaced bright and dark bands. In the experiment, the distance between successive bright fringes (maxima) and dark fringes (minima) is indeed constant. This means that the bright and dark bands are equally spaced.

**Hint**: Consider the formula for fringe spacing, which shows that the distance between maxima and minima is uniform.

3. **Analyzing Option 2**:
The second option claims that the central bright maximum is twice as wide as the other maxima. In reality, while the central maximum is typically the brightest, its width is not necessarily double that of the other maxima. The width of the central maximum is determined by the slit width and the wavelength, but it does not have a fixed relationship of being twice as wide compared to other maxima.

**Hint**: Reflect on how the width of the maxima is defined and how it relates to the slit width and wavelength.

4. **Analyzing Option 3**:
The third option states that the intensity of all bright bands is the same. In Young's double slit experiment, the intensity of the bright fringes can vary depending on the distance from the slits and the amplitude of the light waves. However, for ideal conditions (same amplitude and coherent light), the intensity can be considered uniform across the bright bands.

**Hint**: Think about the conditions under which intensity remains constant across the bright fringes.

5. **Conclusion**:
Based on the analysis:
- Option 1 is correct: The bright and dark bands are equally spaced.
- Option 2 is incorrect: The central maximum is not twice as wide as the others.
- Option 3 is correct: The intensity of all bright bands can be considered the same under ideal conditions.
- Therefore, the correct answer is Option D: both 1 and 3.

### Final Answer:
The correct answer is Option D: both 1 and 3.