Parallel rays of light entering a convex lens always converge at:

Options

A. centre of curvature
B. the principal focus
C. optical centre
D. the focal plane

Explanation

To solve the question "Parallel rays of light entering a convex lens always converge at:", we will follow these steps:

### Step 1: Understand the properties of a convex lens
A convex lens is a transparent optical device that is thicker in the middle and thinner at the edges. It has the ability to converge (bring together) parallel rays of light that pass through it.

**Hint:** Remember that a convex lens is also known as a converging lens.

### Step 2: Identify the behavior of parallel rays of light
When parallel rays of light enter a convex lens, they are refracted (bent) towards the optical axis. This bending occurs due to the change in speed of light as it passes through different mediums (air to glass and back to air).

**Hint:** Think about how light behaves when it passes through different materials.

### Step 3: Determine where the rays converge
The point where these refracted rays meet after passing through the lens is known as the principal focus. This is a key characteristic of convex lenses.

**Hint:** The principal focus is a specific point related to the lens's optical properties.

### Step 4: Conclusion
Thus, parallel rays of light entering a convex lens always converge at the principal focus.

**Final Answer:** The principal focus.