Question

Draw a ray diagram to show the path of the refracted ray in each of the following cases:
A ray of light incident on a concave lens
1. parallel to its principal axis,
2. directed towards its principal focus.

Answer 1

Step 1: Understanding the incident ray parallel to the principal axis:
When a ray of light is incident parallel to the principal axis of a concave lens, it refracts and diverges away from the principal axis.
- The refracted ray appears to originate from the focus (F) on the same side of the lens as the object.
- The divergence is such that if extended backward, the refracted ray would appear to pass through the focal point (virtual focus).

Step 2: Understanding the incident ray directed towards the principal focus:
When a ray of light is directed towards the principal focus of a concave lens, it refracts and travels parallel to the principal axis.
- The refracted ray will move in a direction parallel to the principal axis after passing through the lens.

Step 3: Key properties of the concave lens:
- A concave lens always forms a virtual, upright, and diminished image. - The refracted rays diverge after passing through the lens, and their extensions appear to meet at a point behind the lens, forming a virtual image.

Step 4: Conclusion:
In both cases, the concave lens causes the incident rays to diverge, forming a virtual image that appears to be located on the same side of the lens as the object.