Reflection of light from a perfectly smooth and polished surface, such as a plane mirror, in which parallel incident rays remain parallel after reflection, is specifically called what type of reflection?

Introduction / Context:
This optics question asks you to recall the correct term for reflection from a smooth surface like a mirror. Light can reflect in different ways depending on the nature of the surface. For highly polished surfaces, the reflected rays preserve their relative orientation, producing clear images. Recognising the standard terminology for this type of reflection is important for understanding image formation, mirrors and optical devices.

Given Data / Assumptions:

• The reflecting surface is smooth and polished, like a plane mirror.
• Parallel rays of light fall on the surface.
• After reflection, the rays remain parallel and follow the law of reflection.
• We are asked to name this kind of reflection.

Concept / Approach:
When light falls on a smooth, polished surface, all the microscopic points on the surface have nearly the same orientation. As a result, parallel incident rays are reflected in a single, well defined direction, and the law of reflection (angle of incidence equals angle of reflection) holds at every point. This is called regular reflection or specular reflection. On rough surfaces, irregularities cause the reflected rays to scatter in many directions; this is called diffuse or irregular reflection. Therefore, reflection from a mirror like surface is termed regular reflection.

Step-by-Step Solution:
Step 1: Recall that a plane mirror provides a clear image because reflected rays remain well organised and predictable. Step 2: Understand that this behaviour occurs when the surface irregularities are much smaller than the wavelength of light, making the surface effectively smooth. Step 3: Recognise that this type of reflection is called regular or specular reflection in textbooks. Step 4: Compare with rough surfaces such as walls or paper, where incoming parallel rays are scattered in many directions, giving no clear image; this is diffuse or irregular reflection. Step 5: Since the question refers to a smooth mirror like surface, identify the appropriate term as regular reflection.

Verification / Alternative check:
Think about what happens when you look at yourself in a mirror versus in a sheet of paper. The mirror shows a sharp image due to regular reflection, while the paper does not show an image because it reflects light diffusely. Diagrams of mirror reflection in physics textbooks also label reflection from plane mirrors as regular reflection. This consistent usage confirms that regular is the correct option for a smooth surface.

Why Other Options Are Wrong:
Irregular reflection refers to reflection from rough surfaces where light is scattered in many directions and no clear image is formed. Diffused reflection is another term for irregular reflection and does not describe the mirror like reflection that forms sharp images. Fused reflection is not a standard term in basic optics and does not correspond to any commonly described type of reflection.

Common Pitfalls:
Students sometimes confuse the terms regular and diffuse reflection because both obey the law of reflection at each microscopic point. The key difference is the smoothness of the surface and the overall pattern of reflected rays. Remember that mirrors and shiny metal surfaces produce regular reflection, while walls, cloth and paper produce diffuse reflection. Associating the word regular with mirror like reflection helps you choose the correct option.

Final Answer:
Reflection from a smooth, polished mirror like surface is called regular reflection.