Practice Questions

Q24.A conducting circular loop made of a thin wire has area 3.5 × 10-2 m2 and resistance 10 Ω It is placed perpendicular to a time-dependent magnetic field 𝐵𝑡= 0.4 Tsin50𝜋𝑡 The field is uniform in space. Then the net charge flowing through the loop during 𝑡= 0 s and 𝑡= 10 ms is close to (1) 1.4 𝑚𝐶 (2) 7 𝑚𝐶 (3) 21 𝑚𝐶 (4) 6 𝑚𝐶

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.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.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.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.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 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.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 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.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

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 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.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 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.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.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.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

Q26.In a photoelectric effect experiment, the threshold wavelength of light is 380 nm . If the wavelength of incident light is 260 nm , the maximum kinetic energy of emitted electrons will be Given E (in eV ) = 1237 λ(in nm) (1) 4.5 eV (2) 3.0 eV (3) 1.5 eV (4) 15.1 eV

Q26.If the deBroglie wavelength of an electron is equal to 10− times the wavelength of a photon of frequency 6 × 1014 Hz, then the speed of electron is equal to : (Speed of light = 3 × 108 m/s) Planck's constant = 6.63 × 10−34 J. s Mass of electron = 9.1 × 10−31 kg) (1) 1.1 × 106 m/s (2) 1.7 × 106 m/s (3) 1.8 × 106 m/s (4) 1.45 × 106 m/s

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.The figure shows a Young's double slit experimental setup. It is observed that when a thin transparent sheet of thickness t and refractive index μ is put in front of one of the slits, the central maximum gets shifted by a distance equal to n fringe width. If the wavelength of light used is λ then t will be: (1) Dλ (2) nλ a(μ−1) (μ−1) (3) 2nλ (4) 2Dλ (μ−1) a(μ−1) −

Q26.A convex lens is put 10 𝑐𝑚 from a light source and it makes a sharp image on a screen, kept 10 𝑐𝑚 from the lens. Now a glass block (refractive index 1.5) of 1.5 𝑐𝑚 thickness is placed in between the light source and the JEE Main 2019 (09 Jan Shift 1) JEE Main Previous Year Paper lens. To get the sharp image again, the screen is shifted by a distance 𝑑. Then 𝑑 is: (1) 0 (2) 0.55 𝑐𝑚 away from the lens (3) 0.55 𝑐𝑚 towards the lens (4) 1.1 𝑐𝑚 away from the lens

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

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.The electron in a hydrogen atom first jumps from the third excited state to the second excited state and subsequently to the first excited state. The ratio of the respective wavelengths λ1 of the photons emitted in this λ2 process is: (1) 7 (2) 20 5 7 (3) 9 (4) 27 7 5