Practice Questions

Q21.Consider two thin identical conducting wires covered with very thin insulating material. One of the wires is bent into a loop and produces magnetic field B1 , at its centre when a current I passes through it. The ratio B1 : B2 is: (1) 1:1 (2) 1 : 3 (3) 1 : 9 (4) 9 : 1

Q21.Three straight parallel current carrying conductors are shown in the figure. The force experienced by the middle conductor of length 25 cm is: (1) 3 × 10−4 N toward right (2) 6 × 10−4 N toward right (3) 9 × 10−4 N toward right (4) Zero

Q22.Match List I (Wavelength range of electromagnetic spectrum) with List II (Method of production of these waves) and select the correct option from the options given below the lists. List I List II 700 nm to (a) (i) Vibration of atoms and molecules. 1 mm 1 nm to Inner shell electrons in atoms moving from one (b) (ii) 400 nm energy level to a lower level. (c) < 10−3 nm (iii) Radioactive decay of the nucleus. (d) 1 mm to 0. 1 m (iv) Magnetron valve. (1) (a) - (iii), (b) - (iv), (c) - (i), (d) - (ii) (2) (a) - (i), (b) - (ii), (c) - (iii), (d) - (iv) (3) (a) - (iv), (b) - (iii), (c) - (ii), (d) - (i) (4) (a) - (ii), (b) - (iii), (c) - (iv), (d) - (i)

Q22.A sinusoidal voltage V(t) = 100 sin(500t) is applied across a pure inductance of L = 0.02H. The current through the coil is: (1) 10 cos(500t) (2) −10 cos(500t) (3) 10 sin(500t) (4) −10 sin(500t)

Q23.The diameter of the objective lens of the microscope makes an angle β at the focus of the microscope. Further, the medium between the object and the lens is the oil of the refractive index n. Then the resolving power of the microscope. JEE Main 2014 (19 Apr Online) JEE Main Previous Year Paper (1) Increases with decreasing value of β (2) Increases with increasing value of n sin 2β (3) Increases with increasing value of 1 (4) Increases with decreasing value of n nsin2β

Q23.A diver looking up through the water sees the outside world contained in a circular horizon. The refractive index of water is 4 , and the diver's eyes are 15 cm below the surface of the water. Then the radius of the circle 3 is : (1) 15×√7 3 cm (2) 15×3√7 cm (3) 15 × 3√7 cm (4) 15 × 3 × √5 cm

Q23.A lamp emits monochromatic green light uniformly in all directions. The lamp is 3% efficient in converting electrical power to electromagnetic waves and consumes 100 W of power. The amplitude of the electric field associated with the electromagnetic radiation at a distance of 5 m from the lamp will be nearly: (1) 1.34 V/m (2) 2.68 V/m (3) 4.02 V/m (4) 5.36 V/m

Q24.An object is located in a fixed position in front of a screen. Sharp image is obtained on the screen for two positions of a thin lens separated by 10 cm . The size of the images in two situations are in the ratio 3 : 3. What is the distance between the screen and the object? (1) 124.5 cm (2) 144.5 cm (3) 65.0 cm (4) 99.0 cm

Q24.The refractive index of the material of a concave lens is μ. It is immersed in a medium of refractive index μ1 . A parallel beam of light is incident on the lens. The path of the emergent rays when μ1 > μ is: JEE Main 2014 (12 Apr Online) JEE Main Previous Year Paper (1) (2) (3) (4)

Q24.A ray of light is incident from a denser to a rarer medium. The critical angle for total internal reflection is θiC and Brewster's angle of incidence is θiB , such that sinθiC = η = 1.28 . The relative refractive index of the two sinθiB media is (1) 0.4 (2) 0.2 (3) 0.9 (4) 0.8

Q24.A thin convex lens made from crown glass (μ = 32 ) has focal length f . When it is measured in two different liquids having refractive indices 4 and 5 , it has the focal lengths f1 and f2 respectively. The correct relation 3 3 between the focal lengths is : (1) f1 = f2 < f (2) f1 > f and f2 becomes negative (3) f2 > f and f1 becomes negative (4) f1 and f2 both become negative

Q25.In Young’s double-slit experiment, the distance between the two identical slits is 6. 1 times larger than the slit width. Then the number of intensity maxima observed within the central maximum of the single-slit diffraction pattern is : (1) 3 (2) 6 (3) 24 (4) 12

Q25.A green light is incident from the water to the air - water interface at the critical angle (θc). Select the correct statement. (1) The entire spectrum of visible light will come out (2) The spectrum of visible light whose frequency is of the water at an angle of 90o to the normal less than that of green light will come out to the air medium (3) The spectrum of visible light whose frequency is (4) The entire spectrum of visible light will come out more than that of green light will come out to the of the water at various angles to the normal air medium

Q25.In a compound microscope the focal length of objective lens is 1.2 cm and focal length of eye piece is 3.0 cm. When object is kept at 1.25 cm in front of objective, final image is formed at infinity. Magnifying power of the compound microscope should be: (1) 200 (2) 100 (3) 400 (4) 150

Q26.In an experiment of single slit diffraction pattern, first minimum for red light coincides with first maximum of some other wavelength. If wavelength of red light is 6600Å , then wavelength of first maximum will be: (1) 3300Å (2) 4400Å (3) 5500Å (4) 6600Å JEE Main 2014 (12 Apr Online) JEE Main Previous Year Paper

Q26.Two beams, A and B of plane polarized light with mutually perpendicular planes of polarization are seen through a polaroid. From the position when the beam A has maximum intensity (and beam B has zero intensity), a rotation of polaroid through 30o makes the two beams appear equally bright. If the initial intensities of the two beams are IA and IB respectively, then IAIB equals : (1) 3 (2) 3 2 (3) 1 (4) 1 3

Q27.If the binding energy of the electron in a hydrogen atom is 13. 6 eV , the energy required to remove the electron from the first excited state of Li++ is : (1) 13. 6 eV (2) 3. 4 eV (3) 122. 4 eV (4) 30. 6 eV

Q27.A piece of wood from a recently cut tree shows 20 decays per minute. A wooden piece of the same size placed in a museum (obtained from a tree cut many years back) shows 2 decays per minute. If the half-life of C14 is 5730 years, then the age of the wooden piece placed in the museum is approximately [This question was awarded a bonus and proper correction was made to avoid that] (1) 10439 years (2) 39049 years (3) 19042 years (4) 13094 years

Q28. Given, A and B are input terminals Logic 1 is > 5 V Logic 0 is < 1 V JEE Main 2014 (19 Apr Online) JEE Main Previous Year Paper Which logic gate operation, the following circuit does? Note: This question was awarded a bonus. C option changed. (1) OR gate. (2) NOR gate. (3) Output will always be one. (4) XOR gate.

Q28.An n-p-n transistor has three leads A, B and C. Connecting B and C by moist fingers, A to the positive lead of an ammeter, and C to the negative lead of the ammeter, one finds large deflection. Then, A, B and C refer respectively to : (1) Base, emitter and collector (2) Base, collector and emitter (3) Emitter, base and collector (4) Collector, emitter and base

Q28.Hydrogen (1H1), Deuterium (1H2), singly ionised Helium (2He4)+ and doubly ionised lithium (3Li6)++ all have one electron around the nucleus. Consider an electron transition from n = 2 to n = 1. If the wave lengths of emitted radiation are λ1, λ2, λ3 and λ4 respectively then approximately which one of the following is correct ? (1) 4λ1 = 2λ2 = 2λ3 = λ4 (2) λ1 = 2λ2 = 2λ3 = λ4 (3) λ1 = λ2 = 4λ3 = 9λ4 (4) λ1 = 2λ2 = 3λ3 = 4λ4 JEE Main 2014 (06 Apr) JEE Main Previous Year Paper

Q29.A piece of bone of an animal from a ruin is found to have 14C activity of 12 disintegrations per minute per gm of its carbon content. The 14C activity of a living animal is 16 disintegrations per minute per gm. How long ago nearly did the animal die? (Given half life of 14C is t1/2 = 5760 years) (1) 1672 years (2) 2391 years (3) 3291 years (4) 4453 years

Q29.A radioactive nuclei with decay constant 0.5/s is being produced at a constant rate of 100 nuclei/s. If at t = 0 there were no nuclei, the time when there are 50 nuclei is: (1) 1 s (2) 2 ln ( 43 )s (3) ln 2 s (4) ln ( 34 )s

Q30. In an experiment to determine the gravitational acceleration g of a place with the help of a simple pendulum, the measured time period squared is plotted against the string length of the pendulum in the figure. What is the value of g at the place? (1) 10. 0 m s−2 (2) 9. 87 m s−2 (3) 9. 91 m s−2 (4) 9. 81 m s−2

Q30.A student measured the length of a rod and wrote it as 3.50 cm. Which instrument did he use to measure it ? (1) A meter scale (2) A vernier calliper where the 10 divisions in vernier scale matches with 9 division in main scale and main scale has 10 divisions in 1 cm (3) A screw gauge having 100 divisions in the (4) A screw gauge having 50 divisions in the circular circular scale and pitch as 1 mm scale and pitch as 1 mm