Practice Questions

Q25.In the line spectra of hydrogen atom, difference between the largest and the shortest wavelengths of the Lyman ∘ ∘ series is 305 A . The corresponding difference for the Paschan series in A is:________

Q25.When radiation of wavelength A is used to illuminate a metallic surface, the stopping potential is V . When the same surface is illuminated with radiation of wavelength 3A , the stopping potential is V4 . If the threshold wavelength for the metallic surface is nλ then value of n will be :

Q25.A beam of electromagnetic radiation of intensity 6.4 × 10−5W/cm2 is comprised of wavelength, λ = 310nm . It falls normally on a metal (work function φ = 2eV ) of surface area of 1cm2 . If one in 103 photons ejects an election, total number of electrons ejected in 1s is 10x . (hc = 1240eVnm, 1eV = 1.6 × 10−19J), then x is ___________

Q25.The first member of the Balmer series of hydrogen atom has a wavelength of 6561 A . The wavelength of the second member of the Balmer series (in nm) is_____________

Q25.An observer can see through a small hole on the side of a jar (radius 15 cm ) at a point at height of 15 cm from the bottom (see figure). The hole is at a height of 45 cm. When the jar is filled with a liquid up to a height of 30 cm the same observer can see the edge at the bottom of the jar. If the refractive index of the liquid is N , where N is an integer, the value of N is 100 JEE Main 2020 (03 Sep Shift 1) JEE Main Previous Year Paper

Q25.Orange light of wavelength 6000 × 10–10 m illuminates a single slit of width 0. 6 × 10–4 m. The maximum possible number of diffraction minima produced on both sides of the central maximum is __________

Q25.A part of a complete circuit is shown in the figure. At some instant, the value of current I is 1A and it is decreasing at a rate of 102 As−1 . The value of the potential difference Vp −VQ, (in volts) at that instant is-

Q25.The output characteristics of a transistor is shown in the figure. When VCE is 10V and IC = 4 .0 mA , then value of βac is JEE Main 2020 (06 Sep Shift 2) JEE Main Previous Year Paper

Q25.A point object in air is in front of the curved surface of a plano-convex lens. The radius of curvature of the curved surface is 30 cm and the refractive index of the lens material is 1.5, then the focal length of the lens (in cm) is ___________. 1 − (I) to n2

Q25.The surface of a metal is illuminated alternately with photons of energies E1 = 4 eV and E2 = 2. 5 eV respectively. The ratio of maximum speeds of the photoelectrons emitted in the two cases is 2. The work function of the metal in (eV) is..........

Q25.A beam of electrons of energy E scatters from a target having atomic spacing of 1 Å . The first maximum intensity occurs at θ = 60°. Then E(in eV) is........ (Planck's constant h = 6. 64 × 10−34 Js, 1 eV = 1. 6 × 10−19J, electron mass m = 9. 1 × 10−31 kg)

Q25.In the circuit shown below, is working as a 8 V dc regulated voltage source. When 12 V is used as an input, the power dissipated (in mW ) in each diode is (Considering both zener diodes are identical)

Q25.The balancing length for a cell is 560cm in a potentiometer experiment. When an external resistance of 10Ω is connected in parallel to the cell, the balancing length changes by 60cm . If the internal resistance of the cell is n Ω , where n is an integer then value of n is ________ 10

Q25.When an object is kept at a distance of 30 cm from a concave mirror, the image is formed at a distance of 10 cm from the mirror. If the object is moved with a speed of 9 cm s−1 , the speed (in cm s−1 ) with which image moves at that instant is

Q25.Both the diodes used in the circuit shown are assumed to be ideal and have negligible resistance when these are forward biased. Built in potential in each diode is 0.7V . For the input voltages shown in the figure, the JEE Main 2020 (09 Jan Shift 1) JEE Main Previous Year Paper voltage (in Volts) at point A is ________

Q25.A light ray enters a solid glass sphere of refractive index μ = √3 at an angle of incidence 60°. The ray is both reflected and refracted at the farther surface of the sphere. The angle (in degrees) between the reflected and refracted rays at this surface is _____________.

Q8. At 40°C, a brass wire of 1 mm radius is hung from the ceiling. A small mass, M is hung from the free end of the wire. When the wire is cooled down from 40°C to 20°C it regains its original length of 0.2 m . The value of M is close to: (Coefficient of linear expansion and Young’s modulus of brass are 10-5 /° C and 1011 N / m2, respectively; g = 10 m s-2 ) (1) 0.9 kg (2) 0.5 kg (3) 1.5 kg (4) 9 kg

Q8. Take the mean distance of the moon and the sun from the earth to be 0.4 × 106 km and 150 × 106 km respectively. Their masses are 8 × 1022 kg and 2× 1030 kg respectively. The radius of the earth is 6400 km. Let ΔF1 be the difference in the forces exerted by the moon at the nearest and farthest points on the earth and ΔF2 be the difference in the force exerted by the sun at the nearest and farthest points on the earth. Then, the number closest to ΔF1 is: ΔF2 (1) 2 (2) 6 (3) 10−2 (4) 0.6

Q21.A magnetic needle of magnetic moment 6 .7 × 10-2 A m2 and moment of inertia 7 .5 × 10-6 kg m2 is performing simple harmonic oscillations in a magnetic field of 0 . 01 T. Time taken for 10 complete oscillations is: (1) 8 . 76 s (2) 6 . 65 s (3) 8 . 89 s (4) 6 . 98 s JEE Main 2017 (02 Apr) JEE Main Previous Year Paper

Q22.In a coil of resistance 100 Ω, a current is induced by changing the magnetic flux through it as shown in the figure. The magnitude of change in flux through the coil is: (1) 275 Wb (2) 200 Wb (3) 225 Wb (4) 250 Wb

Q25.In a Young's double slit experiment, slits are separated by 0 . 5 mm, and the screen is placed 150 cm away. A beam of light consisting of two wavelengths, 650 nm and 520 nm, is used to obtain interference fringes on the screen. The least distance from the common central maximum to the point where the bright fringes due to both the wavelengths coincide is: JEE Main 2017 (02 Apr) JEE Main Previous Year Paper (1) 15 . 6 mm (2) 1 . 56 mm (3) 7 . 8 mm (4) 9 . 75 mm 𝑚

Q27.Some energy levels of a molecule are shown in the figure. The ratio of the wavelengths 𝑟= 𝜆1 is given by: 𝜆2, 1 4 (1) 𝑟= (2) 𝑟= 3 3 (3) 𝑟= 2 (4) 𝑟= 3 3 4

Q28.A radioactive nucleus 𝐴 with a half-life 𝑇, decays into a nucleus 𝐵. At 𝑡= 0, there is no nucleus 𝐵. At some time 𝑡, the ratio of the number of 𝐵 to that of 𝐴 is 0.3. Then, 𝑡 is given by: Consider log𝑒𝑥= log𝑥 𝑇 𝑇 log⁡ 2 (1) 𝑡= (2) 𝑡= log⁡1.3 2 log⁡ 1.3 (3) 𝑡= 𝑇log⁡ 1.3 (4) 𝑡= 𝑇log1.3 log⁡ 2

Q4. Concrete mixture is made by mixing cement, stone and sand in a rotating cylindrical drum. If the drum rotates too fast, the ingredients remain stuck to the wall of the drum and proper mixing of ingredients does not take place. The maximum rotational speed of the drum in revolutions per minute (rpm) to ensure proper mixing is close to : (Take the radius of the drum to be 1.25 m and its axle to be horizontal) : (1) 27.0 (2) 0.4 (3) 1.3 (4) 8.0

Q7. In the figure shown ABC is a uniform wire. If the center of mass of the wire lies vertically below point A, then BC is close to AB (1) 1. 85 (2) 1. 5 (3) 1. 37 (4) 3