Light beams alter direction when they are reflected off from a surface, propagate from one transparent medium to another medium, or move through a distinct medium whose composition is continuously varying. The law of reflection describes that when a light ray is reflected from a smooth reflective surface, the reflected angle is equivalent to the incident angle. As per conventions, every angle in geometrical optics is calculated with regard to the normal to the reflecting surface (in other words, to the perpendicular to the given surface). The reflected light ray is always in the plane, which is defined by the normal to the surface and the incident ray. The reflection law can be applied to analyse the images generated by plane mirrors and curved mirrors. In contrast with mirrors, most natural surfaces are predominantly rough on the scale of the light’s wavelength. As a result, parallel incident rays are reflected in numerous varied directions. Diffuse reflection is the reason for the ability to observe most illuminated surfaces from any angle (light rays enter the eyes after reflecting off all sections of the surfaces). Mirrors provide the most typical model for specular reflection of light and are generally composed of a glass sheet along with a smooth metallic coating (most predominant reflections happen here). Reflection is boosted in metals by wave propagation suppression beyond their surface or skin depths. In fact, reflection also happens at the surface of transparent media such as glass or water.
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Reflection of Light Questions and Answers
1) Explain virtual images and real images.
The image location is the position in the region where every reflected light ray appears to diverge or out from. As the reflected light rays appear to diverge from this location, one who observes this image will feel like the actual body is positioned behind the reflecting surface. Here, the concept of the virtual image and real image arises. A virtual image is created when light rays from a single source diverge or spread out after going through an optical lens or after getting reflected. Virtual images are formed at the points where they look to diverge, but as they never really converge, virtual images cannot be cast onto a screen like a projector screen. In contrast, real images are created when the light rays from the reflected light converge or meet at a single point on the later side of the lens. This implies the images being created actually exist since the light rays are converging. Unlike in virtual images, if a projecting screen is positioned in the trajectory of real images, the image will be generated on the screen. Real images are produced by the projectors in the cinema halls. The real images occur where the light beams converge, and virtual images occur where the beams of light appear to join.
2) Why is a real image always inverted?
A real image exists when the light rays converge. Real images are always generated under the principal axis, so these images are always inverted, whereas virtual images are always generated over the principal axis, so these images are always erect.
3) Explain the total internal reflection.
One unique result of the law of refraction is related to light going into a medium with a relatively low refractive index. In this scenario, rays of light are curved away from the normal to the interface between the propagating media. At the critical incidence angle (θ), refracted light rays make an angle of 90° with the normal line. In other words, they skim the edges of the two media. The magnitude of the sine of the critical angle can be easily determined from the refraction law, sin θ = n2/n1.
4) Explain the laws of reflection.
If the reflecting surface is heavily smoothed out, the reflection of light rays that happens is known as regular reflection or specular reflection. The fundamental statements of laws of reflection are given below:
- The incident light ray, the reflected light ray and the normal to the reflecting surface at the point of the incidence are in the same plane.
- The angle that the incident light ray forms with the normal is equivalent to the angle that the reflected ray forms to the same normal.
- The incident and reflected ray are on opposite sides of the normal.
- These three reflection laws can all be generated from the Fresnel equations.
5) What is meant by multiple reflections?
When light beams reflect off a mirror, images appear. When two mirrors are positioned parallelly, this setup gives the appearance of infinite images along a straight line. Countless images appear between the two mirrors that stay at an angle to each other and lie above a circle. The circle’s centre is positioned at the mirrors’ imaginary intersection. A square setup of four mirrors positioned face to face generates the appearance of an infinite set of images oriented in a plane. Numerous images appear between four reflecting mirrors resembling a pyramid, in which every mirror pair stays at an angle to each other and lies above a sphere. If the pyramid’s base has a rectangular shape, the generated images spread over a region of a torus.
6) Give a brief about regular or specular reflection.
Regular or specular reflection is the mirror-like reflection of light rays. In such a kind of reflection, the light rays that are reflected from a shiny and smooth shiny body, such as a normal mirror, are always reflected at a particular angle. All incident light rays which are reflected along with the reflected light ray have the exact angle to the normal as the incident light ray. Therefore, this type of optical process causes the creation of an image.
7) _______ is boosted in metals by wave propagation suppression beyond their surface or skin depths.
Answer: Reflection
Explanation: Reflection is boosted in metals by wave propagation suppression beyond their surface or skin depths.
8) The _______ law can be applied to analyse the images generated by plane mirrors and curved mirrors.
Answer: reflection
Explanation: The reflection law can be applied to analyse the images generated by plane mirrors and curved mirrors.
9) As per conventions, every angle in geometrical optics is calculated with regard to the ______ to the reflecting surface.
Answer: normal
Explanation: As per conventions, every angle in geometrical optics is calculated with regard to the normal to the reflecting surface.
10) The reflected light ray is always in the plane, which is defined by the _______ to the surface and the incident ray.
Answer: normal
Explanation: The reflected light ray is always in the plane, which is defined by the normal to the surface and the incident ray.
11) ______ reflection is the reason for the ability to observe most illuminated surfaces from any angle.
Answer: Diffuse
Explanation: Diffuse reflection is the reason for the ability to observe most illuminated surfaces from any angle.
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Practice Questions
1) What is meant by a mirror?
2) What is the difference between the reflection of light and the refraction of light?
3) What is the main difference between a concave mirror and a convex mirror?
4) What are the applications of total internal reflection?
5) What is the relationship between a lens and a mirror?
6) What is the principle behind the working of a mirror?
Watch the video and solve the previous year questions in the chapter Light Reflection and Refraction Class 10
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