Chapter-12: Geometrical Optics

Chapter-12:  Geometrical Optics

Light is the main focus of this unit which describe different phenomena of light such as reflection, refraction and total internal reflection. This unit explains how images are formed by mirrors and lenses and will discuss working principle of compound microscope and telescope as: 

• describe the terms used in reflection including normal, angle of incidence, angle of reflection and state laws of reflection. 
• solve problems of image location by spherical mirrors by using mirror formula. 
• describe the passage of light through parallel-sided transparent material. 
• define power of a lens and its unit. 
• describe the correction of short-sight and long-sight. 
• solve the problems of image location by lenses using lens formula. 

Short Question Answer
Q-1:	Define Angle of incidence.
Ans:	The angle <i made by the incident ray with the normal is called angle of incidence.
Q-2:	State the conditions for total internal reflection.
Ans:	Conditions: i. Lights rays should travel from denser medium to rare medium. ii. Angle of incidence i. should be larger than critical angle.
Q-3:	What is the Snell' law.
Ans:	Snell’s law: The ration sini/sinr is known as the refractive index of the second medium with respect to the first medium.
Q-4:	Define Angle of reflection:
Ans:	the angel between normal N and the reflected ray OB i.e.
Q-5:	What is the reflection of light?
Ans:	When light travelling in a certain medium falls on a surface of another medium a part of it turns back in the same medium. It is called reflection of light.
Q-6:	Define the refractive index in terms of speed of light.
Ans:	The refractive index ‘n’ of a medium is the ratio of the speed of light ‘c’ in the vacuum to the speed of light ‘v’ in the medium.
Q-7:	What is meant by the term total internal reflection?
Ans:	When a ray of light from denser medium enters a rare medium in such a way that angle of incident is greater than critical angle, then the ray is reflected totally inside and does not emerge out from the denser medium.This phenomenon is called total internal reflection.
Q-8:	What is refraction of light?
Ans:	The process of bending of light as it passes from air into glass and vice versa is called refraction of light.
Q-9:	State and explain laws of reflection.
Ans:	Reflection of light occurs according to following two laws called laws of reflection. i. The incident ray, reflected ray and normal at the point of incidence, all lie in the same plane. ii. The angle of incidence and the angle of reflection are equal. i.e.
Q-10:	State the laws of refraction. What is the Snell' law?
Ans:	i. The incident ray, refracted ray and the normal at the point of incidence all lie in the same plane. ii. The ratio of sine of angle of incidence to the sin of angle of refraction r is always equal to the constant
Q-11:	Define Angle of incidence:
Ans:	The angle between incident ray AO and normal N i.e.
Q-12:	What do you mean by resolving power?
Ans:	Resolving power of an instrument is its ability to distinguish between two closely placed objects or point sources.
Q-13:	Define Radius of curvature:
Ans:	It is the radius of the sphere of which spherical mirror is a part.
Q-14:	Define pole:
Ans:	It is the midpoint of the curved surface of spherical mirror.It is also called vertex.
Q-15:	What is meant by principal concave lens?
Ans:	The light rays travelling parallel to the principal axis of a concave lens after refraction appear to come from a point behind the lens is called principal focus.”F”
Q-16:	What is critical angle?
Ans:	When ray of light travel from denser medium to rare medium then the angle of incidence for which the angle of refraction becomes 90° is called critical angle.
Q-17:	Define Irregular reflection.
Ans:	The reflection by the rough surface is called irregular reflection. e.g. reflection of paper or wall or rough surface.
Q-18:	Define center of curvature:
Ans:	A spherical mirror is a part of a sphere. The center of this sphere is called center of curvature.
Q-19:	Define convex lens.
Ans:	The lens which causes incident parallel rays to converge at a point is known as convex or converging lens. Shape: This lens is thick at the center but thin at the edges.
Q-20:	What is Gastroscopy?
Ans:	The endoscope used to diagnose the stomach is called Gastroscopy.
Q-21:	What is meant by angle of deviation?
Ans:	When a ray is refracted through some refracted surface it deviates from its original path. The angle D made by the deviated ray with the normal is called angle of deviation.
Q-22:	Define Aperture.
Ans:	The size of spherical mirror is called aperture.
Q-23:	How many types of lens.
Ans:	There are two types of lens.
Q-24:	Define concave and diverging lens.
Ans:	The lens which causes incident parallel rays of light to diverge from a point is called concave lens. Shape: This lens is thin at the center and the thick at the edges.
Q-25:	Define principal focus.
Ans:	After reflection from a concave mirror rays of light parallel to the principal axis converge to a point F. this point is called’The principle focus’ of the mirror.
Q-26:	Define Astronomical telescope.
Ans:	Astronomical telescope: i. Objective lens has larger focal length than the eyepiece. ii. Distance between the objective lens and the eyepiece is equal to f0+fe. iii. It is used to see distant astronomical objects.
Q-28:	What is the use of contact lens?
Ans:	Contact lens show the same result as eyeglasses do .These are small thin lenses are placed directly on cornea a thin layer of tears between the lens and cornea keeps the lens in place.
Q-29:	What is pinhole camera?
Ans:	Pinhole camera is simpler than a camera with one lens is a pinhole camera. To make a pinhole camera, a tiny pinhole is made in one side of a box. An inverted real image is formed on the opposite side of the box.
Q-30:	What are geometrical optics?
Ans:	The branch of optics that focuses on the creation of images is called geometrical optics, because it is based on relationship between angles and lines that describe light rays.