Practice Questions

Q21.The velocity of certain ions that pass undeflected through crossed electric field E = 7.7kV/m and magnetic field B = 0.14 T is (1) 18 km/s (2) 77 km/s (3) 55 km/s (4) 1078 km/s

Q22.An electromagnetic wave with frequency ω and wavelength λ travels in the +y direction. Its magnetic field is along +x-axis. The vector equation for the associated electric field (of amplitude E0 ) is JEE Main 2012 (19 May Online) JEE Main Previous Year Paper 2π (1) →E = −E0 cos (ωt + λ y)^x (2) →E = E0 cos (ωt −2πλ y)^x 2π (4) →E = −E0 cos (ωt + (3) →E = E0 cos (ωt −2πλ y)^z λ y)^z

Q22.In an LCR circuit shown in the following figure, what will be the readings of the voltmeter across the resistor and ammeter if an a.c. source of 220 V and 100 Hz is connected to it as shown? JEE Main 2012 (07 May Online) JEE Main Previous Year Paper (1) 800 V, 8 A (2) 110 V, 1.1 A (3) 300 V, 3 A (4) 220 V, 2.2 A

Q22.A radio transmitter transmits at 830kHz. At a certain distance from the transmitter magnetic field has amplitude 4.82 × 10−11 T. The electric field and the wavelength are respectively (1) 0.014 N/C, 36 m (2) 0.14 N/C, 36 m (3) 0.14 N/C, 360 m (4) 0.014 N/C, 360 m

Q22.A resistance R and a capacitance C are connected in series to a battery of negligible internal resistance through a key. The key is closed at t = 0 . If after t sec the voltage across the capacitance was seven times the voltage across R, the value of t is (1) 3RCℓn2 (2) 2RCℓn2 (3) 2RC ln 7 (4) 3RCℓn7

Q23.In Young's double slit experiment, one of the slit is wider than other, so that the amplitude of the light from one slit is double of that from other slit. If Im be the maximum intensity, the resultant intensity I when they interfere at phase difference ϕ is given by (1) Im 9 (4 + 5 cos ϕ) (2) lm3 (1 + 2 cos2 ϕ2 ) (3) Im 5 (1 + 4 cos2 ϕ2 ) (4) Im9 (1 + 8 cos2 ϕ2 )

Q23.Which of the following processes play a part in the formation of a rainbow? (i) Refraction (ii) Total internal reflection (iii) Dispersion (iv) Interference (1) (i), (ii) and (iii) (2) (i) and (ii) (3) (i), (ii) and (iv) (4) (iii) and (iv)

Q23.The frequency of X -rays; γ -rays and ultraviolet rays are respectively a, b and c then (1) a < b; b > c (2) a > b; b > c (3) a < b < c (4) a = b = c

Q23.A glass prism of refractive index 1.5 is immersed in water (refractive index 34 ) as shown in figure. A light beam incident normally on the face AB is totally reflected to reach the face BC, if (1) sin θ > 95 (2) sin θ > 32 (3) sin θ > 98 (4) sin θ > 31

Q24.In a Young's double slit experiment with light of wavelength λ, fringe pattern on the screen has fringe width β. When two thin transparent glass (refractive index μ ) plates of thickness t1 and t2 (t1 > t2) are placed in the path of the two beams respectively, the fringe pattern will shift by a distance (1) β(μ−1 t1 (2) μβ t1 λ t2 λ ( t2 ) (3) β(μ−1 (t1 + t2 ) λ (t1 −t2 (4) (μ −1 λβ )

Q24.A beam of light consisting of red, green and blue colours is incident on a right-angled prism on face AB. The refractive indices of the material for the above red, green and blue colours are 1.39, 1.44 and 1.47 respectively. A person looking on surface AC of the prism will see (1) no light (2) green and blue colours (3) red and green colours (4) red colour only

Q24.Two coherent plane light waves of equal amplitude makes a small angle α(<< 1) with each other. They fall almost normally on a screen. If λ is the wavelength of light waves, the fringe width Δx of interference patterns of the two sets of waves on the screen is (1) 2λ (2) λ α α (3) λ (4) λ (2α) √α

Q24.The first diffraction minimum due to the single slit diffraction is seen at θ = 30∘ for a light of wavelength 5000Å falling perpendicularly on the slit. The width of the slit is (1) 2.5 × 10−5 cm (2) 1.25 × 10−5 cm (3) 10 × 10−5 cm (4) 5 × 10−5 cm

Q25.A telescope of aperture 3 × 10−2 m diameter is focused on a window at 80 m distance fitted with a wire mesh of spacing 2 × 10−3 m. Given: λ = 5.5 × 10−7 m, which of the following is true for observing the mesh JEE Main 2012 (26 May Online) JEE Main Previous Year Paper through the telescope? (1) Yes, it is possible with the same aperture size. (2) Possible also with an aperture half the present diameter. (3) No, it is not possible. (4) Given data is not sufficient.

Q25.Two polaroids have their polarizing directions parallel so that the intensity of a transmitted light is maximum. The angle through which either polaroid must be turned if the intensity is to drop by one-half is (1) 135∘ (2) 90∘ (3) 120∘ (4) 180∘

Q25.The maximum number of possible interference maxima for slit separation equal to 1.8λ, where λ is the wavelength of light used, in a Young's double slit experiment is (1) zero (2) 3 (3) infinite (4) 5

Q26.A hypothetical atom has only three energy levels. The ground level has energy, E1 = −8eV. The two excited states have energies, E2 = −6eV and E3 = −2eV. Then which of the following wavelengths will not be present in the emission spectrum of this atom? (1) 207 nm (2) 465 nm (3) 310 nm (4) 620 nm

Q26.A diatomic molecule is made of two masses m1 and m2 which are separated by a distance r. If we calculate its rotational energy by applying Bohr's rule of angular momentum quantization, its energy will be given by ( n is an integer) (1) (m1+m2)2n2h2 (2) n2h2 2m21m22r2 2(m1+m2)r2 (3) 2n2h2 (4) (m1+m2)n2h2 (m1+m2)r2 2m1m2r2 JEE Main 2012 (Offline) JEE Main Previous Year Paper

Q26.The electron of a hydrogen atom makes a transition from the (n + 1)th orbit to the nth orbit. For large n the wavelength of the emitted radiation is proportional to (1) n (2) n3 (3) n4 (4) n2

Q26.In Young's double slit interference experiment, the slit widths are in the ratio 1 : 25 . Then the ratio of intensity at the maxima and minima in the interference pattern is (1) 3 : 2 (2) 1 : 25 (3) 9 : 4 (4) 1 : 5

Q26.Ionisation energy of Li (Lithium) atom in ground state is 5.4eV . Binding energy of an electron in Li+ ion in ground state is 75.6eV . Energy required to remove all three electrons of Lithium (Li) atom is (1) 81.0eV (2) 135.4eV (3) 203.4eV (4) 156.6eV JEE Main 2012 (19 May Online) JEE Main Previous Year Paper

Q27.The decay constants of a radioactive substance for α and β emission are λα and λβ respectively. If the substance emits α and β simultaneously, then the average half life of the material will be (1) 2TαTβ (2) Tα + Tβ Tα+Tβ (3) TαTβ (4) 1 2 (Tα + Tβ ) Tα+Tβ

Q27.Photoelectrons are ejected from a metal when light of frequency v falls on it. Pick out the wrong statement from the following. (1) No electrons are emitted if v is less than W/h, (2) The ejection of the photoelectrons is where W is the work function of the metal instantaneous. (3) The maximum energy of the photoelectrons is hu.(4) The maximum energy of the photoelectrons is independent of the intensity of the light.

Q27.In the Rutherford experiment, α-particles are scattered from a nucleus as shown. Out of the four paths, which path is not possible? (1) D (2) B (3) C (4) A

Q27.A doubly ionised Li atom is excited from its ground state(n = 1) to n = 3 state. The wavelengths of the spectral lines are given by λ32, λ31 and λ21 . The ratio λ32/λ31 and λ21/λ31 are, respectively (1) 8.1, 0.67 (2) 8.1, 1.2 (3) 6.4, 1.2 (4) 6.4, 0.67