What change is made in the eye to enable it to focus on objects situated at different distances ? Illustrate your answer with the help of diagrams.

Explanation

To understand how the human eye focuses on objects situated at different distances, we need to consider the role of the eye's lens and the ciliary muscles. Here is a step-by-step explanation:

### Step 1: Understanding the Eye Structure
The human eye consists of several important parts, including the cornea, lens, retina, and ciliary muscles. The lens is flexible and can change its shape to focus light onto the retina.

### Step 2: Role of the Lens
The lens of the eye is responsible for focusing light. When light rays enter the eye, they pass through the cornea and the lens before reaching the retina. The lens can change its curvature to adjust the focal length, which allows us to see objects clearly at various distances.

### Step 3: Action of Ciliary Muscles
The ciliary muscles are located around the lens. When these muscles contract or relax, they change the shape of the lens:
- **When focusing on nearby objects**: The ciliary muscles contract, causing the lens to become thicker (more convex). This increases the lens's converging power, allowing it to focus light from close objects onto the retina.
- **When focusing on distant objects**: The ciliary muscles relax, making the lens thinner (less convex). This decreases the lens's converging power, enabling it to focus light from faraway objects onto the retina.

### Step 4: Illustrating the Changes
To illustrate these changes, we can draw two diagrams:
1. **Focusing on a Near Object**:
- Draw an eye with a thick lens and light rays converging to a point on the retina.
- Label the ciliary muscles as contracted.

2. **Focusing on a Distant Object**:
- Draw an eye with a thin lens and light rays converging to a point on the retina.
- Label the ciliary muscles as relaxed.

### Conclusion
The ability of the eye to focus on objects at different distances is due to the action of the ciliary muscles, which alter the shape of the lens. This adjustment changes the focal length of the lens, allowing us to see clearly whether the object is near or far.

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