हिन्दी साहित्य- सीमांचल
|Refraction of Light |
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|Summary |
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|When a ray of light is incident on a boundary separating the two media having different densities: |
|A part of the light gets reflected. |
|Rest of the light changes its direction as it enters the second medium. |
|The change of direction suffered by a ray of light as it passes obliquely from one medium to another is known as refraction |
|Incident Ray |
|The ray of light striking the surface of separation of the media through which it is travelling is known as the incident ray. |
|Point of Incidence |
|The point at which the incident ray strikes the surface of separation is called the point of incidence. |
|Normal |
|The perpendicular drawn to the surface of separation at the point of incidence is called the normal. |
|Refracted Ray |
|The ray of light that has changed its direction at the surface of separation when travelling from one medium to another is called the |
|refracted ray. |
|Angle of Incidence |
|The angle, which the incident ray makes with the normal at the point of incidence, is called the angle of incidence. |
|Angle of Refraction |
|The angle, which the refracted ray makes with the normal at the point of incidence, is called the angle of refraction. |
|Laws of Refraction |
|The laws of refraction are: |
|The incident ray, the refracted ray and the normal to the surface at the point of incidence all lie in one plane. |
|For any two given pair of media, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant. |
|The second law is called Snell's law after the scientist Willebrod Snell who first formulated it |
|[pic] |
|where nm is the refractive index of the second medium with respect to the first medium. |
|Refractive Index |
|Refractive index or absolute refractive index of a medium is equal to the ratio of the speed of light in vacuum or air to the speed of |
|light in that particular medium. |
|[pic] |
|This ratio is always a constant for a given pair of media. |
|Lens |
|A lens is a transparent medium that has at least one curved surface. |
|Convex Lens |
|A convex lens is thicker in the middle and thinner at its edges. |
|Concave Lens |
|A concave lens is thicker at the edges and thinner in the middle. |
|Optic Centre |
|The centre of a lens is called the optical centre or optic centre. It is denoted by the letter O. |
|Centre of Curvature |
|The centres of the spherical surfaces forming a lens are known as the centres of curvature of the lens. The letter C is used to denote |
|centre of curvature. |
|Principal Axis |
|The line passing through the centres of curvature C1 and C2 of two spherical surfaces of the lens is called the principal axis of the |
|lens. |
|Principal Focus of a Convex Lens |
|The principal focus F of a convex lens is a point on the principal axis to which rays parallel to the principal axis converge after |
|refraction. |
|Principal Focus of a Concave Lens |
|The principal focus F of a concave lens is a point on the principal axis from which rays parallel to the principal axis appear to |
|diverge after refraction. |
|Focal Length |
|The distance between the optic centre and the focus is the focal length f of the lens. |
|Rays that are generally considered while constructing ray diagrams: |
|Any ray of light, travelling parallel to the principal axis, after refraction through the lens, passes through the principal focus of |
|the lens. |
|Any ray of light, which first passes through principal focus or which appears to meet at the focus after refraction, always travels |
|parallel to the principal axis. |
|Any ray of light which passes through optical centre of lens does not deviate form its path. |
|The image is formed at the point of intersection of these refracted rays. |
|Sign Convention for Lenses |
|All distances on the principal axis are measured from the optical centre. |
|The distances measured in the direction of incident rays are positive and all the distances measured in the direction opposite to that |
|of the incident rays are negative. |
|All distances measured perpendicular to and above the principal axis are positive. Thus, height of an object and that of an erect image |
|are positive |
|And all distances measured perpendicular to and below the principal axis are negative. |
|Lens Formula |
|[pic] |
|Where u is the object distance or distance of the object from the lens, v is the image distance or the distance of the image from the |
|lens and f is the focal length or the distance of the principal focus from the lens. |
|Magnification |
|It is the ratio of the height of the image to the height of the object. It is represented by the letter m |
|[pic] |
|Magnification produced by a lens is also related to the object distance u, and the image distance v. |
|[pic] |
|Power of a Lens |
|Power of a lens is defined as the reciprocal of its focal length in metres. |
|[pic] |
|The SI unit of power is dioptre |
|1D = 1 m-1 |
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|Question (1): The bending of a beam of light when it passes obliquely from one | |
|medium to another is known as _______. | |
| |Be an International Online Tutor |
|1. |Top of Form |
|reflection |Name |
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|2. | |
|refraction |Email |
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|3. | |
|dispersion |Subject |
| |[pic] |
|4. | |
|deviation |Phone |
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|Ans: 2 |[pic][pic][pic][pic][pic] |
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| |Bottom of Form |
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|Question (2): The part of the lens through which the ray of light passes without |Get tutoring in Math, Algebra, Trigonometry, |
|suffering deviation is called ________. |Geometry, English, Physics, Chemistry and Biology |
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|1. |[pic] |
|optical centre | |
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|2. |Top Clicked |
|focus |tissues gravitation Valence Shell |
| | isotopes science questions types of |
|3. |Respiration photosynthesis online math tutor |
|centre of curvature | |
| |Refraction of Light |
|4. |• |
|pole |Introduction |
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| |Refraction of Light |
|Ans: 1 | |
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| |Laws of Refraction |
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|Question (3): Convex lens always gives a real image if the object is situated |Refraction of Light through a Glass Slab |
|beyond _______. | |
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|1. |Verification of Laws of Refraction - An Alternate |
|optical centre |Method |
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|2. |• |
|centre of curvature |Lenses |
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|3. |• |
|focus |Terminology Used in Optics |
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|4. |• |
|radius of curvature |Formation of Image by a Convex Lens |
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| |Formation of Image by a Concave Lens |
|Ans: 3 | |
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| |Sign Convention for Lenses |
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|Question (4): Parallel rays of light entering a convex lens always converge at |Lens Formula |
|_______. | |
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|1. |Magnification |
|centre of curvature | |
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|2. |Power of a Lens |
|the principal focus | |
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|3. |Summary |
|optical centre | |
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|4. |Question and Answers |
|the focal plane | |
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| |Multiple Choice Questions |
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|Ans: 2 | |
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|Question (5): Where should an object be placed so that a real and inverted image | |
|of the same size is obtained, using a convex lens? | |
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|1. | |
|Between O and F | |
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|2. | |
|At F | |
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|3. | |
|At 2 F | |
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|4. | |
|At infinity | |
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|Ans: 3 | |
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|Question (6): SI unit of the power of a lens is ___________. | |
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|1. | |
|dioptre | |
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|2. | |
|cm | |
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|3. | |
|metre | |
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|4. | |
|watt | |
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|Ans: 1 | |
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|Question (7): 1 D is the power of the lens of focal length of ______ cm. | |
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|1. | |
|100 | |
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|2. | |
|10 | |
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|3. | |
|1/100 | |
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|4. | |
|1/10 | |
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|Ans: 1 | |
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|Question (8): In a simple microscope lens used is __________. | |
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|1. | |
|biconvex | |
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|2. | |
|biconcave | |
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|3. | |
|plano convex | |
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|4. | |
|cylindrical | |
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|Ans: 1 | |
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|Question (9): Reciprocal of focal length in metres is known as the ______ of a | |
|lens. | |
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|1. | |
|focus | |
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|2. | |
|power | |
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|3. | |
|power of accommodation | |
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|4. | |
|far point | |
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|Ans: 2 | |
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|Question (10): A convex lens is called _________. | |
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|1. | |
|converging lens | |
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|2. | |
|diverging lens | |
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|3. | |
|both converging and diverging lens | |
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|4. | |
|refracting lens | |
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|Ans: 1 | |
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|Question (11): A positive magnification greater than unity indicates | |
|_____________________. | |
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|1. | |
|real image | |
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|2. | |
|virtual image | |
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|3. | |
|neither real not virtual image | |
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|4. | |
|distorted image | |
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|Ans: 2 | |
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|Question (12): The power of a convex lens of focal length 50 cm is ______. | |
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|1. | |
|+ 2D | |
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|2. | |
|- 2D | |
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|3. | |
|50 D | |
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|4. | |
|- 5D | |
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|Ans: 1 | |
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|Question (13): The focal length of a lens whose power is -1.5 D is _______. | |
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|1. | |
|-66.66 cm | |
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|2. | |
|+ 1.5 m | |
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|3. | |
|+ 66.66 cm | |
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|4. | |
|-1.5 m | |
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|Ans: 1 | |
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|Question (14): Real images formed by single convex lenses are always | |
|________________. | |
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|1. | |
|on the same side of the lens as the object | |
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|2. | |
|inverted | |
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|3. | |
|erect | |
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|4. | |
|smaller than the object | |
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|Ans: 2 | |
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|Question (15): An object is placed 12 cm from a convex lens whose focal length is | |
|10 cm. The image must be. | |
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|1. | |
|virtual and enlarged | |
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|2. | |
|virtual and reduced in size | |
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|3. | |
|real and reduced in size | |
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|4. | |
|real and enlarged | |
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|Ans: 4 | |
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|Question (16): When a person uses a convex lens as a simple magnifying glass, the | |
|object must be placed at a distance. | |
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|1. | |
|less than one focal length | |
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|2. | |
|more than one focal length | |
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|3. | |
|less than twice the focal length | |
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|4. | |
|more than twice the focal length | |
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|Ans: 1 | |
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|Question (17): The image produced by a concave lens is ________. | |
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|1. | |
|always virtual and enlarged | |
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|2. | |
|always virtual and reduced in size | |
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|3. | |
|always real | |
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|4. | |
|sometimes real, sometimes virtual | |
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|Ans: 2 | |
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|Question (18): A virtual image is formed by _______. | |
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|1. | |
|a slide projector in a cinema hall | |
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|2. | |
|the ordinary camera | |
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|3. | |
|a simple microscope | |
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|4. | |
|telescope | |
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|Ans: 3 | |
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|Question (19): An object is placed 25 cm from a convex lens whose focal length is | |
|10 cm. The image distance is ________ cm. | |
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|1. | |
|50 cm | |
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|2. | |
|16.66 cm | |
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|3. | |
|6.66 cm | |
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|4. | |
|10 cm | |
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|Ans: 2 | |
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|Question (20): The least distance of distinct vision is ______. | |
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|1. | |
|25 cm | |
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|2. | |
|25 m | |
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|3. | |
|0.25 cm | |
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|4. | |
|2.5 m | |
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|Ans: 1 | |
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|Question (21): A convex lens has a focal length of 20 cm. Its power in dioptres is| |
|___________. | |
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|1. | |
|2 | |
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|2. | |
|5 | |
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|3. | |
|0.5 | |
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|4. | |
|0.2 | |
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|Ans: 2 | |
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|Question (22): An object is placed before a concave lens. The image formed | |
|_____________-. | |
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|1. | |
|is always erect | |
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|2. | |
|may be erect or inverted | |
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|3. | |
|is always inverted | |
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|4. | |
|is always real | |
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|Ans: 1 | |
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|Question (23): A ray of light travels from a medium of refractive index n1 to a | |
|medium of refractive index n2. If angle of incidence is i and the angle of | |
|refraction is r. | |
|Then [pic]is equal to | |
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|1. | |
|n1 | |
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|2. | |
|n2 | |
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|3. | |
|n21 | |
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|4. | |
|n12 | |
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|Ans: 3 | |
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|Question (24): Two thin lenses of power +5 D and -2 D are placed in contact with | |
|each other. Focal length of the combination is | |
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|1. | |
|+3 m | |
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|2. | |
|-3 m | |
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|3. | |
|0.33 m | |
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|4. | |
|-0.33 m | |
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|Ans: 3 | |
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|Question (25): The lens formula in cartesian frame is ______________. | |
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|1. | |
|[pic] | |
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|2. | |
|[pic] | |
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|3. | |
|[pic] | |
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|4. | |
|[pic] | |
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|Ans: 3 | |
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|Question (1): Define refraction. | |
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|Answer: The deviation in the path of light when it passes from one medium to another medium of |Be an International Online Tutor |
|different density is called refraction. |Top of Form |
| |Name |
| |[pic] |
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| |Email |
|Question (2): Define refractive index. |[pic] |
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|Answer: The ratio of the speed of light in vacuum to the speed of light in a medium is called |Subject |
|the refractive index of the medium. |[pic] |
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| |Phone |
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|Question (3): What is the unit of refractive index? | |
| |[pic][pic][pic][pic][pic] |
|Answer: Refractive index is the ratio of velocity of light in two media and hence it is a mere | |
|number without any unit. |Bottom of Form |
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| |Get tutoring in Math, Algebra, |
| |Trigonometry, Geometry, English, |
|Question (4): List out the factors on which the refractive index of a medium depends. |Physics, Chemistry and Biology |
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|Answer: The refractive index of a medium depends on |[pic] |
|1) the nature of the medium | |
|2) the colour or wavelength of the incident light | |
| |Top Clicked |
| |tissues gravitation Valence Shell |
| | isotopes science questions types|
| |of |
|Question (5): Define angle of incidence. |Respiration photosynthesis online |
| |math tutor |
|Answer: The angle which the incident ray makes with the normal at the point of incidence is | |
|called the angle of incidence. |Refraction of Light |
| |• |
| |Introduction |
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| |• |
|Question (6): What is the angle of incidence if a ray of light is incident normal to the surface |Refraction of Light |
|separating the two media? | |
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|Answer: Angle of incidence is equal to zero if a ray of light is incident normal to the surface |Laws of Refraction |
|separating the two media. | |
| |• |
| |Refraction of Light through a Glass |
| |Slab |
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|Question (7): What is a lens? |• |
| |Verification of Laws of Refraction -|
|Answer: A lens is a portion of a transparent refracting medium bounded by two spherical surfaces|An Alternate Method |
|which are generally spherical or cylindrical or one curved and one plane surface. | |
| |• |
| |Lenses |
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|Question (8): What is a concave lens? |Terminology Used in Optics |
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|Answer: A lens which is thinner at the middle and thicker at the edges is called a concave lens.|• |
| |Formation of Image by a Convex Lens |
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| |• |
| |Formation of Image by a Concave Lens|
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|Question (9): What is the nature of the focus of a concave lens? | |
| |• |
|Answer: The focus of a concave lens is virtual. |Sign Convention for Lenses |
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| |• |
| |Lens Formula |
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|Question (10): What type of image is formed by a concave lens? |• |
| |Magnification |
|Answer: A concave lens always forms a virtual and erect image. | |
| |• |
| |Power of a Lens |
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| |• |
|Question (11): A thin lens has a focal length f = -12 cm. Is it convex or concave lens? |Summary |
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|Answer: The lens is concave since the focal length is negative. |• |
| |Question and Answers |
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| |• |
| |Multiple Choice Questions |
|Question (12): A lens forms an erect image for all positions of the object in front of it. Is the| |
|lens convex or concave? | |
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|Answer: Concave lens. | |
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|Question (13): Where should an object be placed so that a real and inverted image of same size is| |
|obtained using a convex lens? | |
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|Answer: The object has to be placed at 2F to get a real and inverted image of same size. | |
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|Question (14): Write the relation between u,v and f of a thin lens. | |
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|Answer: | |
|[pic] | |
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|Question (15): What is the sign of u, v and f for a convex lens according to Cartesian sign | |
|convention? | |
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|Answer: According to sign convention u is negative, v is positive for all positions of the | |
|object except when the object is between the optic centre and first focus and f is positive. | |
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|Question (16): An object of height 1m is placed at a distance of 2f from a convex lens. What is | |
|the height of the image formed? | |
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|Answer: The height will also be equal to 1m since the object placed at 2F of a convex lens gives| |
|an image of the same at 2F on the other side of the lens. | |
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|Question (17): Define power. | |
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|Answer: The power of a lens is defined as the reciprocal of its focal length in metres. | |
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|Question (18): What is least distance of distinct vision? | |
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|Answer: The minimum distance upto which an eye can see clearly is called the least distance of | |
|distinct vision. | |
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|Question (19): What happens when a ray of light passes through the optical centre of a lens? | |
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|Answer: The ray of light does not suffer any deviation. | |
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|Question (20): State the laws of refraction. | |
| | |
|Answer: | |
|1) The incident ray, the refracted ray and the normal at the point of incidence all lie in one | |
|plane. | |
|2) For any two given pair of media, the ratio of the sine of the angle of incidence to the sine | |
|of the angle of refraction is a constant. | |
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|Question (21): Diagrammatically represent the refraction of light through a rectangular glass | |
|slab. | |
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|Answer: | |
|[pic] | |
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|Question (22): Define convex lens. Why is it referred to as converging lens? | |
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|Answer: A lens which is thicker in the middle and thinner at the edges is called convex lens. | |
|Convex lens is referred to as a converging lens because the parallel rays of light after | |
|refraction through a convex lens meet at a point on the principal axis. | |
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|Question (23): Draw a diagram to show the second principal focus of a convex lens. | |
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|Answer: | |
|[pic] | |
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|Question (24): Distinguish between a convex and a concave lens. | |
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|Answer: | |
|Convex lens | |
|Concave lens | |
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|Is thicker in the middle and thinner at the edges | |
|Is thinner at the middle and thicker at the edges | |
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|Focus is real | |
|Focus is virtual | |
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|It is a converging lens | |
|It is a diverging lens | |
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|Question (25): Draw a ray diagram to show the refraction of light when it passes through the | |
|optic centre of a convex lens. | |
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|Answer: | |
|[pic] | |
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|Question (26): List out the uses of convex lenses. | |
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|Answer: Convex lenses are used a) as a magnifying glass b) in photocopying cameras c) as the | |
|objective lens of a microscope and a telescope d) in theatre spot lights | |
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|Question (27): With the help of a ray diagram show how an object gets magnified in a simple | |
|microscope. | |
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|Answer: | |
|[pic]When an object is placed between O to F1 we get an enlarged and erect image of the object. | |
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|Question (28): Define the power of a lens. What is its unit? | |
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|Answer: Power of a lens is defined as the reciprocal of its focal length. The unit of power is | |
|dioptre. | |
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|Question (29): With the help of a diagram explain how light gets refracted when it passes through| |
|a rectangular glass slab. | |
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|Answer: | |
|Place a rectangular glass slab on a white sheet of paper fixed on a drawing board. | |
|Trace the boundary ABCD of the glass slab. | |
|Remove the glass slab. Draw an incident ray IO on AB. | |
|Draw the normal NN1 at the point of incidence O | |
|Fix two pins P and Q on the incident ray IO. | |
|Place the glass slab within its boundary ABCD. | |
|Looking from the other side of the glass slab fix two pins R and S such that your eye and the | |
|feet of all the pins are in one straight line. | |
|Remove the glass slab and the pins. Mark the pin points P1, P2, P3 and P4. | |
|Join OO1.It is the refracted ray. | |
|Measure [pic]are the angle of incidence, angle of refraction and angle of emergence respectively.| |
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|[pic] | |
|Extend O1E backwards. The emergent ray is parallel to the incident ray. | |
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|[pic] | |
|The above experiment shows that | |
|When a ray light is passing from air to glass, that is, from a rarer medium to a denser medium, | |
|the refracted ray bends towards the normal drawn at the point of incidence. In this case [pic]But| |
|when the ray of light is passing from glass to air, that is, from a denser to a rarer medium the | |
|refracted ray bends away from the normal. In this case [pic] | |
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|Question (30): An object is placed at a distance of 50 cm from a concave lens of focal length 20 | |
|cm. Find the nature and position of the image. | |
| | |
|Answer: The distance between the object and the lens (u) = -50 cm | |
|Focal length f = -20 cm | |
|Distance of the image from the optic centre = v | |
|[pic] | |
|The image is formed 14.3 cm from the lens on the same side as the object and since v is negative | |
|the image formed is virtual and erect. | |
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|Question (31): An object is placed 50 cm from a lens which produces a virtual image at a distance| |
|of 10 cm in front of the lens. Draw a diagram to show the formation of image and calculate the | |
|focal length of the lens. | |
| | |
|Answer: Distance between the object and the lens = -50cm | |
|Distance between the image and the lens = -10cm | |
|Focal length = ? | |
|[pic] | |
|[pic] | |
|[pic] | |
|[pic] | |
|[pic] | |
|[pic] | |
|The focal length of the lens is -12.5 cm and the negative sign indicates that the lens is | |
|concave. | |
|[pic] | |
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|Question (32): An object of height 4 cm is placed at a distance of 10 cm from a convex lens of | |
|focal length 20 cm. Find the position, nature and size of the image. | |
| | |
|Answer: Distance between the object and the lens u = -10cm | |
|Focal length = f = 20 cm | |
|Distance between the image and the lens v = ? | |
|[pic] | |
|[pic] | |
|[pic] | |
|[pic] | |
|[pic] | |
|[pic] | |
|[pic] | |
|The image is formed on the same side as the object and since v is negative the image is erect and| |
|virtual and is formed at a distance 20 cm in front of the lens. We know that | |
|[pic] | |
|height of the object ho = 4 cm | |
|[pic] | |
|[pic] | |
|[pic] | |
|[pic] | |
|Height of the image = 8 cm | |
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|Question (33): What is the power of a lens having a focal length of a) 50 cm b) -50cm | |
| | |
|Answer: | |
|[pic] | |
|When f = 50 cm | |
|[pic] | |
|[pic] | |
|[pic] | |
|When f = -50 cm | |
|[pic] | |
|[pic] | |
|[pic] | |
|[pic] | |
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|Question (34): Draw a ray diagram to show the position and nature of the image formed by a convex| |
|lens when the object is placed | |
|a) at 2F1 | |
|b) between F1 and 2F1 | |
|c) beyond 2F1 | |
| | |
|Answer: a) at 2F1 | |
|[pic] | |
| | |
|b) between F1 and 2F1 | |
|[pic] | |
| | |
|c) beyond 2F1 | |
|[pic] | |
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|Question (35): State and verify Snell's law. | |
| | |
|Answer: Snell's law states that for any two given pair of media, the ratio of the sine of the | |
|angle of incidence to the sine of the angle of refraction is a constant. | |
|• Place a rectangular glass slab on white sheet of paper fixed on a drawing board. | |
|• Trace the boundary ABCD of the glass slab. | |
|• Remove the glass slab and draw a normal N 1 N 2 at O. | |
|• Draw a straight line IO inclined at an angle say 30 o with the normal. IO is the incident ray.| |
| | |
| | |
|[pic] | |
|Fix two pins P and Q on the incident ray IO. | |
|Place the glass slab within its boundary ABCD. | |
|Looking from the other side of the glass slab fix two other pins R and S such that P, Q, R and S | |
|appear to lie on the same straight line. | |
|Remove the glass slab and the pins. Mark the pin points P, Q, R and S. | |
|Join the pins R and S and produce the line on both sides. The ray O 1 E is the emergent ray. | |
|Join OO 1 . It is the refracted ray. | |
|With O as centre, draw a circle of a convenient radius 'r' in such a way that it cuts the | |
|incident and the refracted rays at F and G respectively. | |
|From F and G draw perpendiculars to the normal N1N2. | |
|Δ FHO and Δ GKO are right angled triangles. | |
|[pic] | |
|Measure the length of FH and GK. | |
|Repeat the experiment for different values of angle of incidence. | |
|Record the result in a tabular form | |
|S. No | |
|I | |
|FH | |
|GK | |
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|[pic] | |
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|1 | |
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|2 | |
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|3 | |
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|4 | |
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|5 | |
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|Find the values of | |
|[pic]for different values of I. | |
|[pic]Will be a constant verifying | |
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