In an astronomical telescope in normal adjustment a straight black line of length `L` is drawn on inside part of objective lens. The eye piece forms a real image of this line. The length of this image is `I`. The magnification of the telescope is

Options

A. `L/l`
B. `L/l + 1`
C. `L/l-1`
D. `(L + l)/(L -l)`

Explanation

To find the magnification of an astronomical telescope in normal adjustment, we can follow these steps:

### Step 1: Understand the Setup
In an astronomical telescope, the objective lens forms a real image of an object (in this case, a straight black line of length \( L \)) which is then viewed through the eyepiece. The length of the image formed by the eyepiece is denoted as \( I \).

### Step 2: Define Magnification
The magnification \( M \) of the telescope can be defined in terms of the lengths of the object and the image. The formula for magnification is given by:

\[ M = \frac{\text{Length of Image}}{\text{Length of Object}} = \frac{I}{L} \]

Where:
- \( I \) is the length of the image formed by the eyepiece.
- \( L \) is the length of the object (the black line).

### Step 3: Substitute Values
From the information given:
- The length of the object is \( L \).
- The length of the image is \( I \).

Substituting these values into the magnification formula:

\[ M = \frac{I}{L} \]

### Step 4: Conclusion
Thus, the magnification of the telescope in normal adjustment is given by:

\[ M = \frac{I}{L} \]