Practice Questions

Q18.In a radioactive material, a fraction of active material remaining after the time t is 9 . The fraction that 16 was remaining after the time t is : 2 (1) 4 (2) 3 5 5 (3) 3 (4) 7 4 8

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.When photon of energy 4.0eV strikes the surface of a metal A, the ejected photoelectrons have maximum kinetic energy TAeV and de-Broglie wavelength λA. The maximum kinetic energy of photoelectrons liberated from another metal B by photon of energy 4.50eV is TB = (TA −1.5)eV. If the de-Broglie wavelength of these photoelectrons λB = 2λA, then the work function of metal B is: (1) 4eV (2) 2eV (3) 1.5eV (4) 3eV

Q19.The radius R of a nucleus of mass number A can be estimated by the formula R = (1. 3 × 10−15)A1/3m . It follows that the mass density of n nucleus is of the order of: (Mprot ≅Mneut ≃1. 67 × 10−27 kg) (1) 103 kg m−3 (2) 1010 kg m−3 (3) 1024 kg m−3 (4) 1017 kg m−3

Q19.An electron (mass m ) with initial velocity →v= v0ˆi + v0ˆj is in an electric filed E = −E0ˆk. If λ0 is initial de- Broglie wavelength of electron, its de-Broglie wave length at time t is given by: (1) λ0√2 (2) λ0 m2v2 0 √1+ e2E2t2m2v20 √1+ e2E2t2 (3) λ0 (4) λ0 m2v2 √1+ e2E2t22m2v20 √2+ e2E2t2 0

Q19.An electron (of mass m ) and a photon have the same energy E in the range of a few eV . The ratio of the de- Broglie wavelength associated with the electron and the wavelength of the photon is ( c = speed of light in vacuum) (1) 1 c ( 2Em ) 1/2 (2) c(2mE)1/2 (3) 1 E 1/2 (4) E 1/2 c ( 2m ) ( 2m )

Q19.Identify the correct output signal Y in the given combination of gates (as shown n) for the given inputs A and B JEE Main 2020 (06 Sep Shift 1) JEE Main Previous Year Paper (1) (2) (3) (4)

Q19.The energy required to ionise a hydrogen like ion in its ground state is 9 Rydbergs. What is the wavelength of the radiation emitted when the electron in this ion jumps from the second excited stale to the ground state? (1) 24. 2nm (2) 11.4nm (3) 35.8nm (4) 8.6nm

Q19.Find the Binding energy per nucleon for 12050Sn. Mass of proton mp = 1. 00783 U , mass of neutron mn = 1. 00867 U and mass of tin nucleus msn = 119. 902199 U . (take 1U = 931 MeV ) (1) 7 .5 MeV (2) 9. 0MeV (3) 8.0MeV (4) 8 .5 MeV

Q19.In a hydrogen atom the electron makes a transition from (n + 1)th level to the nth level. If n >> 1 , the frequency of radiation emitted is proportional to : (1) 1 (2) 1 n n3 (3) 1 (4) 1 n2 n4

Q19.Given figure shows few data points in a photo-electric effect experiment for a certain metal. The minimum energy for ejection of electrons from its surface is: (Planck's constant h = 6.62 × 10–34 J.s) (1) 2.27 eV (2) 2.59 eV (3) 1.93 eV (4) 2.10 eV

Q19.Activities of three radioactive substances A, B and C are represented by the curves A, B and C, in the figure. Then their half-lives T 1 (A) : T 1 (B) : T 1 (C) are in the ratio: 2 2 2 JEE Main 2020 (05 Sep Shift 1) JEE Main Previous Year Paper (1) 2 : 1 : 1 (2) 3 : 2 : 1 (3) 2 : 1 : 3 (4) 4 : 3 : 1

Q19.The time period of revolution of electron in its ground state orbit in a hydrogen atom is 1.6 × 10−16s. The frequency of revolution of the electron in its first excited state (in s−1 ) is: (1) 1.6 × 1014 (2) 7.8 × 1014 (3) 6.2 × 1015 (4) 5.6 × 1012

Q20.Take the breakdown voltage of the zener diode used in the given circuit as 6V . For the input voltage shown in the figure below, the time variation of the output voltage is: (Graphs drawn are schematic and not to the scale) JEE Main 2020 (04 Sep Shift 1) JEE Main Previous Year Paper (1) (2) (3) (4)

Q20.Two Zener diodes ( A and B) having breakdown voltages of 6 V and 4 V respectively, are connected as shown in the circuit below. The output voltage V0 variation with input voltage linearly increasing with time, is given by ( Vinput = 0V at t = 0) (1) (2) (3) (4) JEE Main 2020 (05 Sep Shift 2) JEE Main Previous Year Paper

Q20.The least count of the main scale of a vernier calipers is 1 mm. Its vernier scale is divided into 10 divisions and coincide with 9 divisions of the main scale. When jaws are touching each other, the 7th division of the vernier scale coincides with a division of the main scale and the zero of vernier scale is lying right side of the zero of the main scale. When this vernier is used to measure the length of the cylinder the zero of the vernier scale between 3. 1 cm and 3. 2 cm and 4th VSD coincides with the main scale division. The length of the cylinder is (VSD is vernier scale division) (1) 3. 2 cm (2) 3. 21 cm (3) 3. 07 cm (4) 2. 99 cm

Q20.A student measuring the diameter of a pencil of circular cross-section with the help of a vernier scale records the following four readings 5. 50 mm, 5. 55 mm, 5. 34 mm , 5. 65 mm . The average of these four reading is 5. 5375 mm and the standard deviation of the data is 0. 07395 mm. The average diameter of the pencil should therefore be recorded as : (1) (5 .5375 ±0 .0739) mm (2) (5 .5375 ±0 .0740) mm (3) (5 .538 ±0 .074) mm (4) (5 .54 ±0 .07) mm

Q20.The current i in the network is (1) 0.2 A (2) 0.6 A (3) 0.3 A (4) 0 A

Q20.A screw gauge has 50 divisions on its circular scale. The circular scale is 4 units ahead of the pitch scale marking, prior to use. Upon one complete rotation of the circular scale, a displacement of 0. 5 mm is noticed on the pitch scale. The nature of zero error involved and the lest count of the screw gauge, are respectively: (1) Negative, 2μm (2) Positive 10μm (3) Positive 0. 1mm (4) Positive, 0. 1μm

Q20.The activity of a radioactive sample falls from 700s−1 to 500s−1 in 30 minutes. Its half life is close to: (1) 72min (2) 62min (3) 66min (4) 52min → → → → → → → →

Q21.A body of mass 2 kg is driven by an engine delivering a constant power of 1 J s−1. the body starts from rest and moves in a straight line. After 9 s, the body has moved a distance (in m)….

Q21.The density of a solid metal sphere is diameter. The maximum error in the density of the sphere is ( 100x )%. If the relative errors in measuring the mass and the diameter are 6. 0% and 1. 5% respectively, the value of x is −

Q21.A ball is dropped from the top of a 100 m high tower on a planet. In the last 21 s before hitting the ground, it covers a distance of 19 m. Acceleration due to gravity (in m s−2 ) near the surface on that planet is______

Q21.A small block starts slipping down from a point B on an inclined plane AB, which is making an angle θ with the horizontal section BC is smooth and the remaining section CA is rough with a coefficient of friction μ. It is found that the block comes to rest as it reaches the bottom (point A) of the inclined plane. If BC = 2AC , the coefficient of friction is given by μ = k tanθ . The value of k is ....... JEE Main 2020 (02 Sep Shift 1) JEE Main Previous Year Paper

Q21.A particle (m = 1kg) slides down a frictionless track (AOC) starting from rest at a point A (height 2m ). After reaching C, the particle continues to move freely in air as a projectile. When it reaching its highest point P (height 1m ), the kinetic energy of the particle (in J ) is: (Figure drawn is schematic and not to scale; take g = 10ms−2 ) ______________.