Practice Questions

Q24.A convex lens of focal length 20 cm produces images of the same magnification 2 when an object is kept at two distances x1 and x2(x1 > x2) from the lens. The ratio of x1 and x2 is: (1) 2 : 1 (2) 5 : 3 (3) 4 : 3 (4) 3 : 1

Q24.What is the position and nature of image formed by lens combination shown in figure? ( f1, f2 are focal lengths) (1) 40 cm from point B at right; real (2) 203 cm from point B at right, real (3) 70 cm from point B at right; real (4) 70 cm from point B at left; virtual JEE Main 2019 (12 Jan Shift 1) JEE Main Previous Year Paper

Q25.Calculate the limit of resolution of a telescope objective having a diameter of 200 cm , if it has to detect light of wavelength 500 nm coming from a star. (1) 305 × 10-9 radian (2) 610 × 10-9 radian (3) 152.5 × 10-9 radian (4) 457.5 × 10-9 radian

Q25.The value of numerical aperture of the objective lens of a microscope is 1.25 . If light of wavelength 5000 Å is used, the minimum separation between two points, to be seen as distinct, will be: (1) 0.48 μm (2) 0.24 μm (3) 0.38 μm (4) 0.12 μm

Q25.A concave mirror for face viewing has a focal length of 0.4 m. The distance at which you hold the mirror from your face in order to see your image upright with a magnification of 5 is (1) 1.60 m (2) 0.16 m (3) 0.32 m (4) 0.24 m

Q25.An upright object is placed at a distance of 40 cm in front of a convergent lens of focal length 20 cm . A convergent mirror of focal length 10 cm is placed at a distance of 60 cm on the other side of the lens. The position and size of the final image will be: JEE Main 2019 (08 Apr Shift 1) JEE Main Previous Year Paper (1) 40 cm from the (2) 20 cm from the (3) 40 cm from the (4) 20 cm from the convergent lens, twice convergent mirror, convergent lens, same convergent mirror, the size of the object twice the size of the size of the object same size of the object object

Q25.In a double-slit experiment, green light (5303 A) falls on a double slit having a separation of 19.44μm and a width of 4.05μm. The number of bright fringes between the first and the second diffraction minima is (1) 10 (2) 5 (3) 4 (4) 9

Q25.When a certain photosensitive surface is illuminated with a monochromatic light of frequency ν, the stopping potential of the photo current is −V02 . When the surface is illuminated by monochromatic light of frequency ν 2 , the stopping potential is −V0. The threshold frequency for photoelectric emission is (1) 5v (2) 3v 3 2 (3) 4 v (4) 2v 3

Q25.A plane electromagnetic wave of frequency 50 𝑀𝐻𝑧 travels in free space along the positive 𝑥 - direction. At a particular point in space and time, →𝐸= 6.3 ^𝑗 𝑉/ 𝑚, The corresponding magnetic field →𝐵, at that point will be: (1) 2.1 × 10-8^𝑘 𝑇 (2) 18.9 × 108^𝑘 𝑇 (3) 18.9 × 10-8^𝑘 𝑇 (4) 6.3 × 10-8^𝑘 𝑇

Q25.Consider an electron in a hydrogen atom, revolving in its second excited state (having radius 4.65 Å ). The de- Broglie wavelength of this electron is: (1) 12.9 Å (2) 6.6 Å (3) 9.7 Å (4) 3.5 Å JEE Main 2019 (12 Apr Shift 2) JEE Main Previous Year Paper

Q25.In a Young's double slit experiment slit separation 0.1 mm, one observes a bright fringe at angle 401 rad by using light of wavelength λ1. When the light of wavelength λ2 is used a bright fringe is seen at the same angle in the same set up. Given that λ1 and λ2 are in visible range (380 nm to 740 nm), their values are: (1) 400 nm, 500 nm (2) 380 nm, 525 nm (3) 625 nm, 500 nm (4) 380 nm, 500 nm

Q25.A thin convex lens L (refractive index = 1.5 ) is placed on a plane mirror M. When a pin is placed at A , such that OA = 18 cm, its real inverted image is formed at A itself, as shown in figure. When liquid of refractive index μl is put between the lens and the mirror, the pin has to be moved to A', such that OA' = 27 cm, to get its inverted real image at A' itself. The value of μl will be (1) 4 (2) √3 3 (3) 3 (4) √2 2

Q25.In a young's double slit experiment, the slits are placed 0.320 mm apart. Light of wavelength λ = 500 nm is incident on the slits. The total number of bright fringes that are observed in the angular range −30o ≤θ ≤30o is: (1) 321 (2) 641 (3) 320 (4) 640

Q25.One plano-convex and one plano-concave lens of the same radius of curvature R but of different materials are joined side by side as shown in the figure. If the refractive index of the material of 1 is μ1 and that of 2 is μ2 , JEE Main 2019 (10 Apr Shift 1) JEE Main Previous Year Paper then the focal length of the combination is: (1) R (2) R 2−(μ1−μ2) 2(μ1−μ2) (3) 2R (4) R μ1−μ2 μ1−μ2

Q25.In a Young's double-slit experiment, the ratio of the slit's width is 4 : 1 . The ratio of the intensity of maxima to minima, close to the central fringe on the screen, will be (1) 25 : 9 (2) 9 : 1 4 (3) √3 + 1 : 16 (4) 4 : 1

Q25.In a Young's double slit experiment, the path difference, at a certain point on the screen, betwen two interfering waves is 1 th of wavelength. The ratio of the intensity at this point to that at the centre of a bright fringe is 8 close to: (1) 0.74 (2) 0.85 (3) 0.94 (4) 0.8

Q25.The eye can be regarded as a single refracting surface. The radius of curvature of this surface is equal to that of the cornea (7 .8 mm). This surface separates two media of refractive indices 1 and 1.34 . Calculate the distance from the refracting surface at which a parallel beam of light will come to focus. JEE Main 2019 (10 Jan Shift 2) JEE Main Previous Year Paper (1) 4 .0 cm (2) 1 cm (3) 2 cm (4) 3.07 cm

Q25.A particle A of mass m and charge q is accelerated by a potential difference of 50 V. Another particle B of mass 4m and charge q is accelerated by a potential difference of 2500 V. The ratio of de-Broglie wavelengths λA is close to: λB (1) 0.07 (2) 10.00 (3) 4.47 (4) 14.14

Q26.In an interference experiment the ratio of amplitudes of coherent waves is 𝑎1 = 1 . The ratio of maximum and 𝑎2 3 minimum intensities of fringes will be: (1) 4 (2) 9 (3) 2 (4) 18

Q26.In a double slit experiment, when a thin film of thickness t having refractive index μ is introuduced in front of one of the slits, the maximum at the centre of the fringe pattern shifts by one fringe width. The value of t is ( λ is the wavelength of the light used): (1) λ (2) λ 2 ( μ - 1 ) ( 2μ - 1 ) (3) 2λ (4) λ ( μ - 1 ) ( μ - 1 )

Q26.A convex lens (of focal length 20 cm ) and a concave mirror, having their principal axes along the same lines, are kept 80 cm apart from each other. The concave mirror is to the right of the convex lens. When an object is kept at a distance of 30 cm to the left of the convex lens, its image remains at the same position even if the concave mirror is removed. The maximum distance of the object for which this concave mirror, by itself would produce a virtual image would be: (1) 30 cm (2) 25 cm (3) 20 cm (4) 10 cm JEE Main 2019 (08 Apr Shift 2) JEE Main Previous Year Paper

Q26.In a Frank - Hertz experiment, an electron of energy 5.6 eV passes through mercury vapour and emerges with an energy 0.7 eV . The minimum wavelength of photons emitted by mercury atoms is close to: (1) 250 nm (2) 1700nm (3) 220nm (4) 2020nm

Q26.Consider a Young's double slit experiment as shown in figure. What should be the slit separation d in terms of wavelength λ such that the first minima occurs directly in front of the slit (S1) ? (1) λ (2) λ (5−√2) 2(√5−2) (3) λ (4) λ 2(5−√2) √5−2

Q26.In a photoelectric experiment, the wavelength of the light incident on a metal is changed from 300nm to 400nm. The decrease in the stopping potential is close to : ( hce = 1240nm −V) (1) 0.5 V (2) 1.5 V (3) 1.0 V (4) 2.0 V JEE Main 2019 (11 Jan Shift 2) JEE Main Previous Year Paper

Q26.Diameter of the objective lens of a telescope is 250 cm. For light of wavelength 600 nm coming from a distant object, the limit of resolution of the telescope is close to: (1) 1.5 × 10−7 rad (2) 3.0 × 10−7 rad (3) 2.0 × 10−7 rad (4) 4.5 × 10−7 rad