What is the focal length of a glass slab ?

Options

A. 0
B. infinite
C. 1
D. vary from 0 to 1

Explanation

To determine the focal length of a glass slab, we can follow these steps:

### Step 1: Understanding Light Behavior in a Glass Slab
When light rays from a distant object (considered to be at infinity) strike a glass slab, they enter the slab and travel through it.

### Step 2: Analyzing the Path of Light Rays
The light rays that enter the glass slab are parallel to each other. As they pass through the slab, they do not converge or diverge; they continue to travel in parallel lines.

### Step 3: Observing the Exit of Light Rays
After passing through the glass slab, the rays exit the slab still parallel to each other. This means that there is no focal point where the rays converge.

### Step 4: Conclusion on Focal Length
Since the light rays do not converge at any point after passing through the glass slab, we conclude that the focal length of a glass slab is infinite. This is because the distance from the glass slab to the point where the rays would converge (if they did) is infinitely far away.

### Final Answer
The focal length of a glass slab is infinity.

---