Practice Questions

Q17.An electron, a doubly ionized helium ion ( He++ ) and proton are having the same kinetic energy. The relation between their respective de-Broglie wavelength λe*λHe++ and λp is : (1) λe > λHe++ > λp (2) λe < λHe++ == λp (3) λe > λp > λHe++ (4) λe < λp < λHe++

Q17.A vessel of depth 2h is half filled with a liquid of refractive index 2√2 and the upper half with another liquid of refractive index √2 . The liquids are immiscible. The apparent depth of the inner surface of the bottom of the vessel will be JEE Main 2020 (09 Jan Shift 1) JEE Main Previous Year Paper (1) h (2) h √2 2(√2+1) (3) h (4) 3√2h 3√2 4

Q17.Two sources of light emit X-rays of wavelength 1 nm and visible light of wavelength 500 nm, respectively. Both the sources emit light of the same power 200 W. The ratio of the number density of photons of X-rays to the number density of photons of the visible light of the given wavelengths is: (1) 1 (2) 250 500 (3) 1 (4) 500 250

Q17.A beam of plane polarized light of large cross-sectional area and uniform intensity of 3 .3 W m–2 falls normally on a polarizer (cross-sectional area 3 × 10–4 m2 ), which rotates about its axis with an angular speed of 31 .4 rad s−1 . The energy of light passing through the polarizer per revolution, is close to: (1) 1 .0 ×10−5 J (2) 1. 0 × 10−4 J (3) 1. 5 × 10−4 J (4) 5. 0 × 10−4 J

Q17.A thin lens made of glass (refractive index = 1.5 ) of focal length f = 16cm is immersed in a liquid of refractive index 1.42 . If its focal length in liquid is fl , then the ratio fl/f is closest to the integer: (1) 1 (2) 9 (3) 5 (4) 17

Q17.The electric field of a plane electromagnetic wave is given by E = E0(ˆx + ˆy) sin(kz −ωt). Its magnetic field will be given by (1) E0 c (−ˆx + ˆy) sin(kz −ωt) (2) E0c (ˆx + ˆy) sin(kz −ωt) (3) E0 c (ˆx −ˆy) sin(kz −ωt) (4) E0c (ˆx −ˆy) cos(kz −ωt)

Q17.A spherical mirror is obtained as shown in the figure from a hollow glass sphere, if an object is positioned in front of the mirror, what will be the nature and magnification of the image of the object? (Figure down as schematic and not to scale) JEE Main 2020 (02 Sep Shift 1) JEE Main Previous Year Paper (1) Inverted, real and magnified (2) Erect, virtual and magnified (3) Erect, virutual and unmagnified (4) Inverted, real and unmagnified

Q17.There is a small source of light at some depth below the surface of water (refractive index = 43 ) in a tank of large cross sectional surface area. Neglecting any reflection from the bottom and absorption by water, JEE Main 2020 (09 Jan Shift 2) JEE Main Previous Year Paper percentage of light that emerges out of surface is (nearly): [Use the fact that surface area of a spherical cap of height h and radius of curvature r is 2πrh ] (1) 21% (2) 34% (3) 17% (4) 50%

Q17.A square loop of side 2a, and carrying current I is kept in XZ plane with its centre at origin. A long wire carrying the same current I is placed parallel to the z-axis and passing through the point (0, b, 0), (b >> a). The magnitude of the torque on the loop about z-axis is given by. (1) μ0I 2a2 (2) μ0I 2a3 2πb 2πb2 (3) 2μ0I2a2 (4) 2μ0I2a3 πb πb2

Q17.When the wavelength of radiation falling on a metal is changed from 500 nm to 200 nm, the maximum kinetic energy of the photoelectrons becomes three times larger. The work function of the metal is close to: JEE Main 2020 (03 Sep Shift 1) JEE Main Previous Year Paper (1) 0. 81 eV (2) 1. 02 eV (3) 0. 52 eV (4) 0. 61 eV

Q17.The magnifying power of a telescope with tube length 60cm is 5. What is the focal length of its eye piece? (1) 20cm (2) 40cm (3) 30cm (4) 10cm

Q17.An object is gradually moving away from the focal point of a concave mirror along the axis of the mirror. The graphical representation of the magnitude of linear magnification (m) versus distance of the object from the mirror (x) is correctly given by (Graphs are drawn schematically and are not to scale) JEE Main 2020 (08 Jan Shift 2) JEE Main Previous Year Paper (1) (2) (3) (4)

Q17.For a plane electromagnetic wave, the magnetic field at a point x and time t is : → B(x, t) = T. [1 .2 ×10−7 sin(0 .5 ×103x + 1 .5 ×1011t)ˆk] → → The instantaneous electric field E corresponding to B is : → → (1) (2)V V E(x, t) = E(x, t) = [−36 sin(0. 5 × 103x + 1. 5 × 1011t)ˆj] m [36 sin(1 × 103x + 0. 5 × 1011t)ˆj] m → → (3) (4)V V E(x, t) = E(x, t) = [36 sin(0. 5 × 103x + 1. 5 × 1011t)ˆk] m [36 sin(1 × 103x + 15 × 1011t)ˆi] m

Q17.A polarizer - analyser set is adjusted such that the intensity of light coming out of the analyser is just 36% of the original intensity. Assuming that the polarizer - analyser set does not absorb any light, the angle by which JEE Main 2020 (07 Jan Shift 1) JEE Main Previous Year Paper the analyser needs to be rotated further, to reduce the output intensity to zero, is (sin−1( 35 ) = 37°) (1) 53o (2) 37o (3) 90o (4) 45o

Q17.In a Young's double slit experiment, 16 fringes are observed in a certain segment of the screen when light of wavelength 700 nm is used. If the wavelength of light is changed to 400 nm, the number of fringes observed in the same segment of the screen would be : (1) 24 (2) 30 (3) 18 (4) 28

Q18.A double convex lens has power P and same radii of curvature r of both the surfaces. The radius of curvature of a surface of a plano-convex lens made of the same material with power 1. 5 P is : JEE Main 2020 (06 Sep Shift 2) JEE Main Previous Year Paper (1) 2R (2) R2 (3) 3R (4) R 2 3 ¯

Q18.In a photoelectric effect experiment, the graph of stopping potential V versus reciprocal of wavelength obtained is shown in the figure. As the intensity of incident radiation is increased : JEE Main 2020 (04 Sep Shift 2) JEE Main Previous Year Paper (1) Straight line shifts to right (2) Slope of the straight line get more steep (3) Straight line shifts to left (4) Graph does not change

Q18.You are given that 73Li = 7. 0160u,Mass of Mass of 42He = 4. 0026u and Mass of 11He = 1. 0079H When 20g of 73Li is converted into 42 He by proton capture, the energy liberated, (in kWh ), is : [Mass of nucleon = 1 GeV /c2 ] (1) 4. 5 × 105 (2) 8 × 106 (3) 6. 82 × 105 (4) 1. 33 × 106

Q18.For a concave lens of focal length f , the relation between object and image distance u and v, respectively, from its pole can best be represented by ( u = v is the reference line): (1) (2) (3) (4)

Q18.Two coherent sources of sound, S1 and S2, produce sound waves of the same wavelength λ = 1 m are in phase. S1 and S2 are placed 1. 5 m apart (see fig). A listener, located at L, directly in front of S2, finds that the intensity is at a minimum when he is 2 m away from S2. The listener moves away from S1, keeping the distance from S2 fixed. The adjacent maximum of intensity is observed when the listener is at a distance d from S1. Then d is : (1) 12m (2) 5m (3) 2m (4) 3m

Q18.Particle A of mass mA = m2 moving along the x -axis with velocity v0 collides elastically with another particle B at rest having mass mB = m3 . If both the particles move along the x -axis after the collision, the change Δλ in the wavelength of the particle A , in terms of its de-Broglie wavelength (λ0) before the collision is: (1) Δλ = 32 λ0 (2) Δλ = 52 λ0 (3) Δλ = 2λ0 (4) Δλ = 4λ0

Q18.The aperture diameter of a telescope is 5m . The separation between the moon and the earth is 4 × 105km . With light of wavelength of 5500Å , the minimum separation between objects on the surface of moon, so that they are just resolved, is close to: (1) 60m (2) 20m (3) 200m (4) 600m

Q18.In a Young’s double slit experiment, the separation between the slits is 0.15mm . In the experiment, a source of light of wavelength 589nm is used and the interference pattern is observed on a screen kept 1.5m away. The separation between the successive bright fringes on the screen is: (1) 6.9mm (2) 3.9mm (3) 5.9mm (4) 4.9mm

Q18.Visible light of wavelength 6000 × 10−8cm falls normally on a single slit and produces a diffraction pattern. It is found that the second diffraction minimum is at 60o from the central maximum. If the first minimum is produced at θ1, then θ1 is close to (1) 20o (2) 30o (3) 25o (4) 45o

Q18.A particle is moving 5 times as fast as an electron. The ratio of the de-Broglie wavelength of the particle to that of the electron is 1. 878 × 10–4 . The mass of the particle is close to : (1) 4. 8 × 10−27 kg (2) 9. 1 × 10−31 kg (3) 1. 2 × 10−28 kg (4) 9. 7 × 10−28 kg