3 RefractionThe phenomena due to which a ray of light deviates from its path, at the surface of separation of two media, when the ray of light is travelling from one optical medium to another, is called refraction of light.
5 Laws of Refraction (Snell’s Law) The incident ray, refracted ray and normal at the point of incidence lie on the same planeThe ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant for a pair of given media. This constant is called the Refractive Index of the second medium, with respect to the first. It’s represented by 1µ2 or 1n2
6 Refraction through Prism ∠i = Angle of incidence∠i1 = Angle of Emergence∠δ = Angle of Deviation
8 DispersionThe phenomenon due to which white light splits into seven colours after passing through an equilateral prism, is called dispersion.Note: If an equilateral prism is placed in an inverted manner adjacent to the above prism, it can recombine the colours to form white light.
12 Major Terms related to a lens Centre of CurvaturePrincipal AxisOptical CentrePrincipal FocusFocal LengthAperture
13 Real v/s Virtual ImageReal images are formed by actual intersection of light raysThey are always invertedVirtual images are formed when rays of light appear to meetThey are always erect
14 Step-wise guide for construction of ray diagrams for Convex lens Construct a straight horizontal line as the principal axis of the lensAt the midpoint of the line mark the optical centre of the lens as the point ‘O’ O
15 From optical centre with the focal length, mark the principal focus on the principal axis, on either side of ‘O’F O FMark the centre of curvature at a distance of 2xfocal length from the optical centre on either side and mark them as 2F2F F O F F
16 From optical centre construct a perpendicular dotted line which will serve as the axis of the lens and draw the lens2F F F FO
17 Construct the object and draw a ray from top of the object and make it pass through the point O and extend it further2F F F FO
18 Construct another ray parallel to the principal axis, after reaching the lens, bend the ray and make it pass through the focus. The place where the two rays meet, construct the image2F F F FO
19 Step-wise guide for construction of ray diagrams for Concave lens Construct a straight horizontal line as the principal axis of the lensAt the midpoint of the line mark the optical centre of the lens as the point ‘O’ O
20 From optical centre with the focal length, mark the principal focus on the principal axis, on either side of ‘O’F O FMark the centre of curvature at a distance of 2xfocal length from the optical centre on either side and mark them as 2F2F F O F F
21 From optical centre, construct a perpendicular dotted line which will serve as the axis of the lens and draw the lens2F F F FO
22 Construct the object and draw on ray from top of the object and make it pass through the point O and extend it furtherF2F F FO
23 Construct a ray parallel to principal axis, and make it meet at the lens. F2F F FO
24 Draw dotted lines from the focus to the meeting point of the surface of the lens and extend it further in bold lineAt the point of intersection of the two rays, draw the image in dotted linesF2F F FO
25 Quick NotesRay of light passing through optical centre always go undeviatedRay of light parallel to principal axis, meets at the focus after passing through a convex lensRay of light parallel to principal axis, diverges out of the focus after passing through a concave lensConcave lens always forms a virtual imageVirtual rays and images are always to be constructed in dotted lines.
26 Lens, image & characteristics ObjectImageCharecteristicsConvexAt InfinityAt FReal. Diminished to a point, InvertedBeyond 2FBetween F & 2FReal, Diminished, InvertedAt 2FReal, Same size as object, InvertedBetween F and 2FReal, Magnified, InvertedBetween O and FOn same side of objectVirtual, Magnified, ErectConcaveAt infinityFocus on same side of objectVirtual, diminished to a point, ErectAnywhere between O and infinityOn same side of object between F and OVirtual, diminished, Erect
27 M.C. KEJRIWAL VIDYAPEETH DEPT. OF PHYSICS CLASS VIII, SESSIONWORKSHEET - 1
28 InstructionsThe worksheet consists of seven questions in the next two slidesThe worksheet is to be solved in the Physics exercise booksStudents may take print outs of the questions given in the following slides and paste in the copyOtherwise the student may copy the questions in the exercise book and then solve the worksheetThe last date for submission of the worksheet is 4th May, 2015
29 WorksheetUnder what conditions light ray will not change its direction when it passes from one optical medium to another optical medium?A ray of light passes from medium A to medium B. The angle of incidence is 35o and angle of refraction is 20o. Which medium is denser, A or B?Why refractive index of any medium is always greater than one?Draw ray diagram for the image formation by a convex lens when the object beyond 2F but not at infinity.
30 Draw ray diagram for the image formation by a convex lens when the object is at principal focus. The focal length of the convex lens used as magnifying glass should have preferably longer or shorter focal length.Which two rays remain parallel when passed through a glass block?