Practice Questions

Q18.An arc lamp requires a direct current of 10 A at 80 V to function. If it is connected to a 220 V (rms), 50 Hz AC supply, the series inductor needed for it to work is close to: (1) 0.044 H (2) 0.065 H (3) 80 H (4) 0.08 H

Q19.Arrange the following electromagnetic radiations per quantum in the order of increasing energy: A : Blue light B : Yellow light C : X-ray D : Radiowave (1) C, A, B, D (2) B, A, D, C (3) D, B, A, C (4) A, B, D, C

Q19.A conducting metal circular-wire-loop of radius r is placed perpendicular to a magnetic field which varies with τ , where B0 and τ are constants at time t = 0 . If the resistance of the loop is R , then the time as B = B0e−t heat generated in the loop after a long time (t →∞) is 0 (1) π2r4B4 0 (2) π2r4B2 2τR 2τR (3) π2r4B20R (4) π2r4B20 τ τR

Q19.A magnetic dipole is acted upon by two magnetic fields which are inclined to each other at an angle of 75o . One of the fields has a magnitude of 15 mT. The dipole attains stable equilibrium at an angle of 30o with this field. The magnitude of the other field (in mT) is close to (1) 1 (2) 11 (3) 36 (4) 1060

Q20.Consider a thin metallic sheet perpendicular to the plane of the paper moving with speed v in a uniform magnetic field B going into the plane of the paper (see figure). If charge densities σ1 and σ2 are induced on the left and right surfaces respectively of the sheet, then (ignore fringe effects) (1) σ1 = −ϵ02 vB , σ2 = ϵ0 2vB (2) σ1 = ϵ0 vB, σ2 = −ϵ0 vB (3) σ1 = ϵ0 2vB , σ2 = −ϵ02 vB (4) σ1 = σ2 = ϵ0 vB

Q20.A series LR circuit is connected to a voltage source with V (t) = V0 sin(ωt) . After a very large time, current I(t) behaves as (t0 ≫LR ): JEE Main 2016 (09 Apr Online) JEE Main Previous Year Paper (1) (2) (3) (4)

Q20.An observer looks at a distant tree of height 10 m with a telescope of magnifying power of 20. To the observer, the tree appears as (1) 20 times taller. (2) 20 times nearer. (3) 10 times taller. (4) 10 times nearer. JEE Main 2016 (03 Apr) JEE Main Previous Year Paper

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.Consider an electromagnetic wave propagating in vacuum. Choose the correct statement: JEE Main 2016 (10 Apr Online) JEE Main Previous Year Paper (1) For an electromagnetic wave propagating in +y (2) For an electromagnetic wave propagating in + y → → direction the electric field is E = 1 Eyz(x, t)ˆz direction the electric field is E = 1 Eyz(x, t)ˆy √2 √2 → 1 → 1 and the magnetic field is B = Bz(x, t)ˆy and the magnetic field is B = Byz(x, t)ˆz √2 √2 (3) For an electromagnetic wave propagating in + x (4) For an electromagnetic wave propagating in + x direction the electric field is direction the electric field is → → E = 1 Eyz(y, z, t) (ˆy + ˆz) and the magnetic E = 1 Eyz(x, t) (ˆy −ˆz) and the magnetic field √2 √2 → → field is B = 1 Eyz(y, z, t) (ˆy + ˆz) is B = 1 Byz(x, t)(ˆy + ˆz) √2 √2

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.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 )

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

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

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 )

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

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

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.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.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.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

Q26.If a, b, c, d are inputs to a gate and x is its output, then, as per the following time graph, the gate is: (1) OR (2) NAND (3) NOT (4) AND

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