If numerical aperture of a microscope is increased, then its

Options

A. Resolving power remains constant
B. Resolving power becomes zero
C. Limit of resolution is decreased
D. Limit of resolution is increased

Answer

To solve the question regarding the effect of increasing the numerical aperture (NA) of a microscope on its resolving power and limit of resolution, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Numerical Aperture (NA)**:
- The numerical aperture of a microscope is a dimensionless number that characterizes the range of angles over which the system can accept or emit light. It is defined as:
\[ NA = n \cdot \sin(\theta) \]
where \( n \) is the refractive index of the medium in which the lens is working (usually air or immersion oil) and \( \theta \) is the half-angle of the maximum cone of light that can enter or exit the lens.

2. **Effect of Increasing NA**:
- When the numerical aperture is increased, either by increasing the refractive index of the medium or by increasing the angle \( \theta \), the microscope can gather more light. This increased light-gathering ability allows for better illumination of the specimen.

3. **Understanding Resolving Power**:
- The resolving power of a microscope is its ability to distinguish between two closely spaced objects. It is inversely related to the limit of resolution (D), which can be expressed as:
\[ D = \frac{1.22 \cdot \lambda}{NA} \]
where \( \lambda \) is the wavelength of light used.

4. **Analyzing the Limit of Resolution**:
- From the formula, we can see that as the numerical aperture (NA) increases, the limit of resolution (D) decreases. This means that the microscope can resolve smaller distances between two points, thus improving its resolving power.

5. **Conclusion**:
- Therefore, if the numerical aperture of a microscope is increased, the limit of resolution decreases, which means the resolving power of the microscope increases.

### Final Answer:
- The correct option is that the limit of resolution is **decreased**.