Geometrical Optics

• Reflection of light is the phenomenon where a part of light travelling in a certain medium falls on the surface of another medium, turning back in the same medium.
• The two laws of reflection are: the incident ray, the reflected ray, and the normal all lie in the same plane, and the angle of incidence is equal to the angle of reflection (i.e., i = r).
• Like plane surfaces, spherical surfaces also reflect light satisfying the two laws of reflection.
• In mirrors, image formation takes place through reflection of light while in lenses image is formed through refraction of light.
• The equation relating the distance of the object p from the mirror/lens, distance of the image q and the focal length f of the mirror/lens is called mirror/lens formula, given by.
• Magnification of a spherical mirror or thin lens is defined as “the ratio of the image height to the object height.” i.e.,
• Power of a lens is defined as “the reciprocal of its focal length in metres” i.e., Power of a lens = P = 1 / focal length in metres.
• The SI unit of power of a lens is “Dioptre”, denoted by a symbol D.
• If f is expressed in metres so that 1 Dioptre is the power of a lens whose focal length is 1 metre.
• The refractive index ‘n’ of a material is the ratio of the speed of light ‘c’ in air to the speed of light ‘v’ in the material, thus.
• The bending of light from its straight path as it passes from one medium into another is called refraction.
• Refraction of light takes place under two laws called laws of refraction: the incident ray, the refracted ray, and the normal at the point of incidence all lie in the same plane, and the ratio of the sine of the angle of incidence ‘i’ to the sine of the angle of refraction ‘r’ is always equal to a constant i.e., = constant.
• The angle of incidence for which the angle of refraction becomes 90 is called critical angle.
• When the angle of incidence becomes larger than the critical angle, no refraction occurs and the entire light is reflected back into the denser medium, this is known as total internal reflection of light.
• A simple microscope, also known as a magnifying glass, is a convex lens which is used to produce magnified images of small objects.
• A compound microscope is used to investigate structure of small objects and has two converging lens, the objective and the eyepiece.
• Telescope is an optical instrument which is used to observe distant objects using lenses or mirrors.
• A telescope that uses two converging lenses is called refracting telescope.
• A telescope in which the objective lens is replaced by a concave mirror is called reflecting power telescope.
• The magnifying power is defined as “the ratio of the angle subtended by the image as seen through the optical device to that subtended by the object at the unaided eye”.
• The resolving power of an instrument is its ability to distinguish between two closely placed objects.
• The ability of the eye to change the focal length of its lens so as to form a clear image of an object on its retina is called its power of accommodation.
• The disability of the eye to form distinct images of distant objects on its retina is known as nearsightedness.
• Nearsighted eye can be corrected with glass or contact lenses that use diverging lenses.
• The disability of the eye to form distinct images of nearby objects on its retina is known as farsightedness.
• Farsightedness can be corrected with the aid of a suitable converging lens.
• Reflection of Light

  A) Angle of incidence

  B) Angle of reflection

  C) Normal N

  D) Plane Mirror

  E) Point of Incidence

  F) Incident Ray

  G) Reflected Ray

  
• Types of Spherical Mirrors

  A) Principal Axis

  B) Radius of Curvature

  C) Centre of Curvature

  D) Pole

  E) Radius of Curvature

  F) Principal Axis

  G) Centre of Curvature

  H) Pole

  I) Concave Mirror

  J) Convex Mirror

  
• Refraction of Light

  A) Incident Ray

  B) Reflected Ray

  C) Refracted Ray

  D) Angle of incidence

  E) Normal N

  F) Angle of refraction

  G) Air (Rarer)

  H) Glass (Denser)

  
• Condition for Total Internal Reflection

  A) Air

  B) Glass

  C) Incident Ray

  D) No refracted Ray

  E) Reflected Ray

  F) i > c

  
• Passage of Light through Optical Fibre: Light is passed through the core of the optical fibre.

  A) cladding n = 1.39

  B) core n = 1.53

  C) cladding n = 1.39

  D) r

  E) i > c

  F) air n = 1.00

  
• Image Formation by Lenses

  A) Object beyond 2F

  B) Object at 2F

  C) Object between F and 2F

  D) Object at F

  E) Object between F and lens

  
• Ray Diagram of Image in a Magnifying Glass: The image is formed by the light rays passing through the lens.

  A) convex lens

  B) object

  C) principle axis

  D) image

  E) light rays

  F) eye

  
• Parts of a Compound Microscope: Objective lens, stage, stage light, stage slide, eyepiece lens, eyepiece

  A) Eyepiece

  B) Body Tube

  C) Revolving Nose Piece

  D) Objective

  E) Mirror

  F) Base

  G) Inclination Joint

  H) Course Adjustment Knob

  I) Fine Adjustment Knob

  
• Important Features of Compound Microscope: It gives greater magnification than a single lens. the objective lens has a short focal length, so the image is focused at a short distance from the objective lens (fo < 1cm). The eyepiece has a larger focal length, (fo of a few cm)
• Human Eye Accommodation: The process of changing the shape of the lens to focus on near or distant objects.

  A) Distant Object

  B) Relaxed Lens

  C) Image on Retina

  D) Close Object

  E) Tensed Lens

  F) Image on Retina

  
• Nearsightedness/Shortsightedness/Myopia: The eye is too short and cannot focus on distant objects clearly

  A) Distant Object

  B) Far point of nearsighted eye

  C) Relaxed Lens

  D) Image formed infront of retina

  E) Virtual Image formed by diverging lens

  F) Diverging lens

  G) Image formed on retina

  
• Farsightedness/Longsightedness/Hypermetropia: The inability to focus on near objects.

  A) near point of farsighted eye

  B) object

  C) Tensed Lens

  D) image formed behind retina

  E) virtual image formed by converging lens

  F) converging lens

  G) Image formed on retina