Principal ray travel

### The principal ray travels parallel to the principal axis before hitting the lens. It is refracted through the principal focus.

## Step1: Understanding Principal Ray### The principal ray is a line that is used to determine the path of light through a lens or mirror. It is defined as the line that travels parallel to the principal axis of a lens or mirror.## Step2: Principal Ray Travels Parallel to Principal Axis### The principal ray, before it hits the lens, travels in a direction that is parallel to the principal axis. The principal axis is an imaginary line that passes through the center of the lens or mirror.## Step3: Refraction of Principal Ray### When the principal ray hits the lens, it is refracted or bent. The direction of refraction is such that the ray emerges through the principal focus of the lens. The principal focus is a point on the principal axis at which all rays parallel to the principal axis converge after passing through the lens.