[Physics Class Notes] on A Single Concept to Explain Everything in Ray Optics Plane Mirrors

Ray Optics is also known as geometrical optics. Ray Optics represents a model of optics that describes light propagation in terms of rays. In Ray Optics, an obstruction or barrier is used for interfering with the path along which light propagates under certain circumstances. Ray Optics is not accountable for specific optical effects such as diffraction and interference. This simplification is very well used when the size of the structure with which the light interacts is bigger than the wavelength. Generally this technique is used in explaining the geometrical aspects of imaging, including optical aberrations.

The simplifying assumptions of Ray Optics say that light rays:

• Must propagate in a straight-line path when they are present in a homogeneous medium.

• In some circumstances, must bend or may have to split in two, at the interface between the two different media.

• Must follow curved paths in a medium where the refractive index fluctuates.

• Must get absorbed or reflected.

Laws of Ray Optics

The Ray Optics or the geometrical optics are based upon three laws.

• The law of rectilinear propagation: It says that light travels in a straight line.

• The law of reflection: It states that when a ray of light gets reflected on a surface separating two optical media, the reflected ray remains within the incidence plane. The angle of incidence is same as that of the angle of reflection. The plane of incidence is the plane where the incident ray and the surface normal is present at the point of incidence.

• The law of refraction: It states that when a ray of light is refracted at an interface separating two optical media, the transmitted ray stays within the plane of incidence, and the sine of the angle of incidence gets directly proportional to the sine of the angle of refraction.

Plane Mirror

A ray optics plane mirror is a mirror consisting of a flat reflective surface. When light rays strike the plane mirror, the angle of reflection is equal to the angle of incidence. The angle of incidence is the angle between the surface normal and the incident ray. The surface normal is the imaginary line that is perpendicular to the surface. The angle of reflection is the angle between the surface normal and the reflected ray. A collimated beam of light never spreads out after getting reflected from a ray optics plane mirror except in case of diffraction effects.

The above image shows how the light rays reflect in a plane mirror and produce a virtual image

Preparation

A ray optics plane mirror is made up of using a highly reflecting and polished surface such as a silver or aluminum surface in a process known as silvering. After completing the silvering process, a thin layer of red lead is to be applied at the mirror’s back. The reflecting surface reflects most of the light rays striking it as long as its surface is not contaminated by tarnishing or oxidation. 

Recently, the modern mirrors are being designed with a thin plate glass that prevents and strengthens the mirror surface and prevents the surface from tarnishing. In the past, mirrors were merely flat pieces of polished copper, obsidian, brass, or precious metal. A mirror is made from a liquid such as the elements gallium and mercury, as they are very highly reflective in their liquid state.

Characteristics of Images Formed By Plane Mirror

The characteristics of the images formed by the ray optics plane mirror are:

• The image is always virtual.

• The image is erect and of the same size and shape as the object.

• The distance of the object from the plane mirror is the same as the distance of the image from the plane mirror.

• The image in the plane mirror is inverted, which means when you are raising your left hand, it would appear in the ray optics plane mirror that you have raised your right hand.

Real Image

Some of its properties are:

• A real image is capable of being seen on the screen.

• A real image is always inverted.

• A real image is formed when the light ray, after going through reflection and refraction, meet at the same point.

• A real image is formed when rays of light actually get intersected.

Virtual Image

Properties of a virtual image are:

• It cannot be obtained on the screen.

• A virtual image is always erect.

• A virtual image is formed when light rays appear to meet at a point.

• A virtual image is formed with the imaginary intersection of light rays.