Chapter -9 class 12 physics
Questions on refractive index and snells law-
Q.1 Can absolute refractive index of any medium be less than unity?
Q.2 Can relative refractive index of mediums be less than unity?
Q.3 Do the frequency and wavelength change when light passes from rarer to denser medium?
Q.4 If refractive indices of glass and water with respect to air are 3/2 and 4/3 respectively. What is the refractive index of glass with respect to water.
Q.5 A small Inc dot on a paper is viewed through a glass slab of thickness 10 cm and refractive index 1.5 by what distance would that dot appear to be raised. Ans 3.33cm
Q.6 A ray of light is incident at an angle of 45° on one face of a rectangular glass slab of thickness 10 cm and refractive index 1.5 calculate the lateral shift produced. Ans 0.033m
Q.7 What is the apparent position of an object below rectangular block of glass 6 cm thick if a layer of water 4 cm thick is on the top of the glass? ng= 3/2 and nw= 4/3
Q.8 A ray of light is incident on a transparent glass slab of refractive index √3. If the reflected and refracted rays are mutually perpendicular. What is the angle of incidence. Ans. 60°
Q.9 On what factors does the lateral shift in glass slab depends?
Q.10 Find a lateral shift of a light ray while it passes through a parallel glass slab of thickness 3√3 cm placed in air. The angle of incidence in air is 60° and the angle of the refraction in glass is 30°. Ans 3cm
Questions on critical angle and total internal reflection
Q.11State the conditions for the phenomenon of total internal reflection to occur.
Q.12 Velocity of light in a liquid is 1.5×10^ 8 m/s and in air it is 3×10^ 8 m/s. If a ray of light passes from liquid into air calculate the value of critical angle? Ans.30°
Q.13 Determine the critical angle for a glass air interface, if a ray of light which is incident in air on the surface is deviated through 15°, when its angle of incidence is 40°. Ans. 41.1°
Q.14 One face of a prism of refractive index 1.5 and angle 75° is covered with a liquid of refractive index 3 √2/4. What should be the angle of incidence of light on the clear face of prism for which light is just totally reflected at the liquid covered face? Ans= sin^-1(3/4) = i= 48.6°
Q.15 Find the angle of refraction in a medium whose refractive index is 2 if light is incident in vacuum, making an angle equal to twice the critical angle. Ans. Sin^-1 √3/4
Questions on Refraction at spherical surfaces
Q.16 A mark placed on the surface of a sphere is viewed through a glass from a position directly opposite. If the diameter of the sphere is 10 cm and refractive index of glass is 1.5 find the position of the image Ans. v= -20cm
Q.17 Light from a point source in air falls on spherical glass of refractive index 1.5 and radius= 0.2 m the image is formed at a distance of 100cm from the glass surface in the direction of incident light. Calculate the object distance from the centre of curvature of the spherical surface. Ans. 120cm
Q.18 Light from a point source in air falls on a spherical glass surface. If refractive index is 1.5, and radius of curvature is 20 cm, the distance of light source from the glass surface is 100cm, at what position will image be formed? Ans. v= 100cm
Questions on Len’s Makers formula and lens formula
Q.19 Biconvex lens has a focal length 2/3 times the radius of curvature of either surface. Calculate the refractive index of lens material. Ans. n= 1.75
Q.20 Find the radius of curvature of convex surface of a Plano convex lens has focal length is 0.3 m and refractive index equal to 1.5. Ans. -0.15m
Q.21 A magician during a show makes a glass lens n= 1.5 disappear in a trough of liquid. What is the refractive index of the liquid? Is the liquid water?
Questions on combination of lenses
Q.22 Two lenses of power +15Dand -5D are in contact with each other forming lens combination a) What is the focal length of this combination? b) an object of size 3 cm is placed at 30 cm from this combination of lenses. Calculate the position and size of the image formed. 10cm, -1.5cm
Q.23 A convex lens is placed in contact with a convex lens of focal and 25 cm. The combination produces a real image at a distance of 80 cm, when an object is at a distance of 40 cm. What is the focal length of concave lens? -400cm
Q.24 i) If f= +0.5 m, what is the power of the lens? ii) the radii of curvature of the faces of a double convex lens are 9 cm and 15 cm. Its focal length is 12 cm. What is the refractive index of glass?iii) a convex lens has 20 cm focal length in air. What is the focal length in water? Refractive index of air water=1.33, refractive index of air glass =1.5
Q.25A convex lens is place in contact with the plane mirror. An axial point object at a distance of 20 cm from this combination, has its image coinciding with itself. What is the focal length of convex lens? 20cm
Q.26 A convex lens of focal length 20 cm is placed coaxially with a convex mirror of radius of curvature 20 cm. The two are kept 15 cm apart from each other. A point object is placed 60 cm in front of the convex lens. Find the position of the image formed by the combination. 30cm
Question on Microscope
Q. If we need a magnification of 375 from a microscope of tube length 15 cm and an objective of focal length 0.5 cm, what focal length of a lens should be used? Ans. 2.2cm
Q. A man with normal near point reads a book with small print using a magnifying glass a thin convex lens of focal length 5 cm. A )what are the closest and the farthest distances at which he can read the book when viewing through the magnifying glass? B) what is the maximum and the minimum angular magnification is possible using the above simple microscope. Ans. u= -4.2 cm ( closest) , u'= -5cm (farthest), 6 and 5
Q. A compound microscope has an objective of focal length 1 cm and and eyepiece of focal length 2.5 cm. An object has to be placed at a distance of 1.2 cm away from the objective for normal adjustment. Find the angular magnification and length of the microscope tube. Ans. Vo= 6cm, m= -50 L= 8.5
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