Quiz 1. Reflection is the process in which light strikes a surface and bounces off that surface. The reflected ray will bounce back directly to the light source if it is lined up with the ...
a. incident ray
b. reflected ray
c. normal line
d. reflecting surface
Answer) c.
Quiz 2. When you attempt to focus an image on a screen, using a concave mirror, but cannot, yet, you can see an image when are looking into the same concave mirror, the image is called a ...
a. convex distortion
b. concave image
c. virtual image
d. reflected distortion
Answer) c
When a mirror cannot focus an image on a screen, but you can see an image in the mirror, it is called a virtual image
Law of Reflection Simulation
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REFLECTION OF LIGHT
Suppose you have just had your hair cut and you want to know what the back of your head looks like. You can do this seemingly impossible task by using two mirrors to direct light from behind your head to your eyes. Redirecting light with mirrors reveals a basic property of light’s interaction with matter.
Light traveling through a uniform substance, whether it is air, water, or a vacuum, always travels in a straight line. However, when the light encounters a different substance, its path will change. If a material is opaque to the light, such as the dark, highly polished surface of a wooden table, the light will not pass into the table more than a few wavelengths. Part of the light is absorbed, and the rest of it is deflected at the surface. This change in the direction of the light is called reflection. All substances absorb at least some incoming light and reflect the rest. A good mirror can reflect about 90 percent of the incident light, but no surface is a perfect reflector.
The texture of a surface affects how it reflects light
The manner in which light is reflected from a surface depends on the surface’s smoothness. Light that is reflected from a rough, textured surface, such as paper, cloth, or unpolished wood, is reflected in many different directions, as shown in Fig 1(a). This type of reflection is called diffuse reflection.
Light reflected from smooth, shiny surfaces, such as a mirror or water in a pond, is reflected in one direction only, as shown in Fig 1(b). This type of reflection is called specular reflection. A surface is considered smooth if its surface variations are small compared with the wavelength of the incoming light.
For our discussion, reflection will be used to mean only specular reflection.
(a) (b)
Fig 1. Diffusely reflected light is reflected in many directions (a), whereas specularly reflected light is reflected in the same forward direction only (b).
(a)
(b)
Fig 2. The symmetry of reflected light (a) is described by the law of reflection, which states that the angles of the incoming and reflected rays are equal (b).
Incoming and reflected angles are equal
You probably have noticed that when incoming rays of light strike a smooth reflecting surface, such as a polished table or mirror, at an angle close to the surface, the reflected rays are also close to the surface.When the incoming rays are high above the reflecting surface, the reflected rays are also high above the surface. An example of this similarity between incoming and reflected rays is shown in Fig 2(a).
If a straight line is drawn perpendicular to the reflecting surface at the point where the incoming ray strikes the surface, the angle of incidence and the angle of reflection can be defined with respect to the line. Careful measurements of the incident and reflected angles q and q , respectively, reveal that the angles are equal, as illustrated in Fig 2(b).
(angle of incidence : the angle between a ray that strikes a surface and the line perpendicular to that surface at the point of contact
angle of reflection : the angle formed by the line perpendicular to a surface and the direction in which a reflected ray moves)
$ \theta = \theta' $
angle of incoming light ray = angle of reflected light ray
The line perpendicular to the reflecting surface is referred to as the normal to the surface. It therefore follows that the angle between the incoming ray and the surface equals 90° − $ \theta$, and the angle between the reflected ray and the surface equals 90° − $ \theta'$ .