where A and B are constants. Plot a graph showing the dependence of µon λ. Ans: How does power of lens vary when incident red light is replaced by blue light? Wavelength decreases hence power increases Ans: An object is held at the principal focus of a concave lens of focal length Where is the image f. formed? Ans: That is image will be formed between optical centre and focus of lens; towards the side of the object. What is the geometrical shape of the wavefront when a plane wave passes through a convex lens? Ans: The wavefront is spherical of decreasing radius. What is the angle between the plane of polariser and analyser, in order that the intensity of transmitted through analyser reduces to half? Ans: 450 A diverging lens of focal length is cut into two identical parts each forming a plano-concave lens. ‘F’ What is the focal length of each part? Ans: Focal length of each half part will be twice the focal length of initial diverging lens. How the angular separation of interference fringes in double slit experiment change when Young’s the distance between the slits and screen is doubled? Ans: Angular separation between fringes, = where = wavelength, = separation between λ/d λ d θ coherent sources. So, is independent of distance between the slits and screen. So angular θ separation (θ ) will remain unchanged. Two thin lenses of power +6 D and 2 D are in contact. What is the focal length of the combination? – Net power of lens combination P = P1 + P2 = + 6 D - 2 D = + D Ans: Focal length, f = 1/P = ¼ m = 25 cm ∴ How does the angular separation between fringes in single-slit diffraction experiment change when the distance of separation between the slit and screen is doubled? Ans: Angular separation is = / D = / d θ β λ Since is independent of angular separation would remain same. θ D, 12. How does the fringe width, in double-slit experiment, change when the distance of Young’s separation between the slits and screen is doubled? Ans: The fringe width is, = / d β D λ
where A and B are constants. Plot a graph showing the dependence of µon λ. Ans: How does power of lens vary when incident red light is replaced by blue light? Ans: Wavelength decreases hence power increases An object is held at the principal focus of a concave lens of focal length f. Where is the image formed? Ans: That is image will be formed between optical centre and focus of lens; towards the side of the object. What is the geometrical shape of the wavefront when a plane wave passes through a convex lens? Ans: The wavefront is spherical of decreasing radius. What is the angle between the plane of polariser and analyser, in order that the intensity of transmitted through analyser reduces to half? Ans: 450 A diverging lens of focal length ‘F’ is cut into two identical parts each forming a plano-concave lens. What is the focal length of each part? Ans: Focal length of each half part will be twice the focal length of initial diverging lens. How the angular separation of interference fringes in Young’s double slit experiment change when the distance between the slits and screen is doubled? Ans: Angular separation between fringes, θ = λ/d where λ = wavelength, d = separation between coherent sources. So, θ is independent of distance between the slits and screen. So angular separation (θ ) will remain unchanged. Two thin lenses of power +6 D and – 2 D are in contact. What is the focal length of the combination? Ans: Net power of lens combination P = P1 + P2 = + 6 D - 2 D = + D ∴ Focal length, f = 1/P = ¼ m = 25 cm How does the angular separation between fringes in single-slit diffraction experiment change when the distance of separation between the slit and screen is doubled? Ans: Angular separation is θ = β / D = λ / d Since θ is independent of D, angular separation would remain same. 12. How does the fringe width, in Young’s double-slit experiment, change when the distance of separation between the slits and screen is doubled? Ans: The fringe width is, β = D λ / d
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