Practice Questions

Q21.Microwave oven acts on the principle of: (1) giving rotational energy to water molecules (2) giving translational energy to water molecules (3) giving vibrational energy to water molecules (4) transferring electrons from lower to higher energy levels in water molecule

Q21.In an experiment for determination of refractive index of glass of a prism by i v/s δ plot, it was found that a ray incident at angle 35o , suffers a deviation of 40o and that it emerges at angle 79o . In that case which of the following is closest to the maximum possible value of the refractive index? (1) 1.7 (2) 1.8 (3) 1.5 (4) 1.6

Q22.To find the focal length of a convex mirror, a student records the following data: Object pin Convex Lens Convex Mirror Image Pin 22.2 cm 32.2 cm 45.8 cm 71.2 cm The focal length of the convex lens is f1 and that of mirror is f2 . Then taking index correction to be negligibly small, f1 and f2 are close to: (1) f1 = 7.8 cm f2 = 12.7 cm (2) f1 = 12.7 cm f2 = 7.8 cm (3) f1 = 15.6 cm f2 = 25.4 cm (4) f1 = 7.8 cm f2 = 25.4 cm

Q22.To determine refractive index of glass slab using a travelling microscope, minimum number of readings required are : (1) Two (2) Four (3) Three (4) Five

Q22.The box of a pin hole camera, of length L, has a hole of radius a. It is assumed that when the hole is illuminated by a parallel beam of light of wavelength λ the spread of the spot (obtained on the opposite wall of the camera) is the sum of its geometrical spread and the spread due to diffraction. The spot would then have its minimum size (say bmin ) when: and bmin = √4λL (1) a = √λL and bmin = √4λL (2) a = λ2L and bmin = (3) a = λ2L ( 2λ2L ) (4) a = √λL and bmin = ( 2λ2L )

Q23.Radiation of wavelength λ is incident on a photocell. The fastest emitted photoelectron has a speed v . If the 3λ wavelength is changed to , the speed of the fastest emitted photoelectron will be 4 4 2 (1) = v( 1 1 3 ) 2 (2) = v( 34 ) 2 (3) > v( 3 1 1 4 ) 2 (4) < v( 43 )

Q23.A convex lens, of focal length 30 cm, a concave lens of focal length 120 cm, and a plane mirror are arranged as shown. For an object kept at a distance of 60 cm from the convex lens, the final image, formed by the combination, is a real image, at a distance of: (1) 60 cm from the convex lens (2) 60 cm form the concave lens (3) 70 cm from the convex lens (4) 70 cm from the concave lens

Q23.A hemispherical glass body of radius 10 cm and refractive index 1.5 is silvered on its curved surface. A small air bubble is 6 cm below the flat surface inside it along the axis. The position of the image of the air bubble made by the mirror is seen : (1) 14cm below flat surface (2) 20cm below flat surface (3) 16cm below flat surface (4) 30cm below flat surface

Q24.Half-lives of two radioactive elements A and B are 20 minutes and 40 minutes, respectively. Initially, the samples have an equal number of nuclei. After 80 minutes, the ratio of decayed numbers of A and B nuclei will be: (1) 1 : 4 (2) 5 : 4 (3) 1 : 16 (4) 4 : 1

Q24.In Young's double-slit experiment, the distance between slits and the screen is 1 m and monochromatic light of wavelength 600 nm is being used. A person standing near the slits is looking at the fringe pattern. When the JEE Main 2016 (09 Apr Online) JEE Main Previous Year Paper separation between the slits is varied, the interference pattern disappears for a particular distance d0 between the slits. If the angular resolution of the eye is 1 ° , then the value of d0 is close to 60 (1) 1 mm (2) 3 mm (3) 2 mm (4) 4 mm

Q24.Two stars are 10 light years away from the earth. They are seen through a telescope of objective diameter 30 cm. The wavelength of light is 600nm. To see the stars just resolved by the telescope, the minimum distance between them should be (1 light year = 9.46 × 1015m) of the order of : (1) 108km (2) 1010km (3) 1011km (4) 106km

Q25.A photoelectric surface is illuminated successively by monochromatic light of wavelengths λ and λ2 . If the maximum kinetic energy of the emitted photoelectrons in the second case is 3 times that in the first case, the work function of the surface is : (1) hc (2) hc 2λ λ (3) hc (4) 3hc 3λ λ

Q25.When photons of wavelength λ1 are incident on an isolated sphere, the corresponding stopping potential is found to be V . When photons of wavelength λ2 are used, the corresponding stopping potential was thrice that of the above value. If light of wavelength λ3 is used then find the stopping potential for this case: (1) hc + 1 − + 1 − λ2 λ1 2λ2 λ1 e [ λ31 1 ] (2) hce [ λ31 1 ] (3) hc − 1 − + 1 − λ2 λ1 e [ λ31 1 ] (4) hce [ λ31 3 ] 2λ2 2λ1

Q25.For a common emitter configuration, if α and β have their usual meanings, the correct relationship between α and β is: β β2 (1) α = 1+β (2) α = 1+β2 (3) α 1 = β1 −1 (4) α = 1−ββ

Q26.A neutron moving with a speed 'v' makes a head on collision with a stationary hydrogen atom in ground state. The minimum kinetic energy of the neutron for which perfactly inelastic collision will take place is : (1) 20.4 eV (2) 10.2 eV (3) 12.1 eV (4) 16.8 eV

Q26.An electron in a hydrogen atom makes a transition from n = 2 to n = 1 and emits a photon. This photon strikes a doubly ionized lithium atom which was already in an excited state and completely removes the orbiting electron. The least quantum number for the excited state of the lithium-ion for the process is (1) 2 (2) 4 (3) 5 (4) 3

Q27.An unknown transistor needs to be identified as a npn or pnp type. A multimeter, with +ve and -ve terminals, is used to measure resistance between different terminals of transistor. If terminal 2 is the base of the transistor then which of the following is correct for a pnp transistor? (1) +ve terminal 2, -ve terminal 3, resistance low (2) +ve terminal 2, -ve terminal 1, resistance high (3) +ve terminal 1, -ve terminal 2, resistance high (4) +ve terminal 3, -ve terminal 2, resistance high

Q27.The ratio (R) of output resistance r0, and the input resistance ri in measurements of input and output characteristics of a transistor is typically in the range : JEE Main 2016 (10 Apr Online) JEE Main Previous Year Paper (1) R~102 −103 (2) R~1 −10 (3) R~0.1 −1.0 (4) R~0.1 −0.01

Q28.To get an output of 1 from the circuit shown in the figure the input must be: (1) a = 0, b = 0, c = 1 (2) a = 1, b = 0, c = 0 (3) a = 1, b = 0, c = 1 (4) a = 0, b = 1, c = 0

Q28.A Zener diode with a breakdown voltage of 4 V is connected in series with a resistance R to a battery of emf 10 V . The maximum power dissipation rating for the Zener diode is 1 W. The value of R to ensure maximum power dissipation across the diode is (1) 12 Ω (2) 24 Ω (3) 36 Ω (4) 6 Ω

Q29.The truth table given in fig. represents: A B Y 0 0 0 0 1 1 1 0 1 1 1 1 (1) OR-Gate (2) NAND-Gate (3) AND-Gate (4) NOR-Gate

Q30.A modulated signal Cm(t) has the form Cm(t) = 30 sin 300πt + 10(cos 200πt −cos 400πt). The carrier frequency f ′c the modulating frequency(message frequency) fω and the modulation index μ are respectively given by : (1) fc = 200 Hz; fm = 50 Hz ; μ = 21 (2) fc = 150 Hz; fm = 50 Hz ; μ = 32 (3) fc = 150 Hz; fm = 30 Hz ; μ = 13 (4) fc = 200 Hz; fm = 30 Hz ; μ = 21

Q30.An audio signal consists of two distinct sounds: one a human speech signal in the frequency band of 200 Hz to 2700 Hz, while the other is a high frequency music signal in the frequency band of 10200 Hz to 15200 Hz. The ratio of the AM signal band width required to send both the signals together to the AM signal band width required to send just the human speech is: JEE Main 2016 (09 Apr Online) JEE Main Previous Year Paper (1) 3 (2) 5 (3) 6 (4) 2

Q1. If the capacitance of a nanocapacitor is measured in terms of a unit u, made by combining the electronic charge e, Bohr radius a0, Planck's constant h and speed of light c then hc u = (1) u = e2a0hc (2) e2a0 (3) u = e2c (4) u = e2h ha0 ca0

Q1. The period of oscillation of a simple pendulum is T = 2π√lg 1 mm accuracy and time for 100 oscillations of the pendulum is found to be 90 s using a wristwatch of 1 s resolution. The accuracy in the determination of g is (1) 5% (2) 4% (3) 3% (4) 1%