Practice Questions

Q16.Hysteresis loops for two magnetic materials A and B are given below: These materials are used to make magnets for electric generators, transformer core and electromagnet core. Then it is proper to use: (1) A for transformers and B (2) B for electromagnets and transformers. for electric generators. (3) A for electric generators and transformers. (4) A for electromagnets and B for electric generators.

Q17.Two identical wires A and B, each of length l, carry the same current I . Wire A is bent into a circle of radius R and wire B is bent to form a square of side a . If BA and BB are the values of magnetic field at the centres of the circle and square respectively, then the ratio BA is BB (1) π2 (2) π2 16 8√2 (3) π2 (4) π2 8 16√2

Q17.To know the resistance G of a galvanometer by half deflection method, a battery of emf VE and resistance R is used to deflect the galvanometer by angle θ . If a shunt of resistance S is needed to get half deflection the G, R and S are related by the equation: (1) S(R + G) = RG (2) 2S(R + G) = RG (3) 2G = S (4) 2S = G

Q18.A 50 Ω resistance is connected to a battery of 5 V . A galvanometer of resistance 100 Ω is to be used as an ammeter to measure current through the resistance, for this a resistance rS is connected to the galvanometer. Which of the following connections should be employed if the measured current is with in 1% of the current without the ammeter in the circuit? (1) rS = 0.5Ω in series with galvanometer (2) rS = 1 Ω in series with galvanometer (3) rS = 1 Ω in parallel with galvanometer (4) rS = 0.5 Ω in parallel with the galvanometer

Q18.A fighter plane of length 20 m, wing span (distance from tip of one wing to the tip of the other wing) of 15 m and height 5 m is flying towards east over Delhi. Its speed is 240 ms−1. The earth's magnetic field over Delhi is 5 × 10−5T with the declination angle ~0o and dip of θ such that sin θ = 32 . If the voltage developed is VB between the lower and upper side of the plane and VW between the tips of the wings then VB and VW are close to : (1) VB = 40 mV ; VW = 135 mV with left side of (2) VB = 45 mV ; VW = 120 mV with right side of pilot at higher voltage pilot at higher voltage (3) VB = 40 mV ; VW = 135 mV with right side of (4) VB = 45 mV ; VW = 120 mV with left side of pilot at high voltage pilot at higher voltage

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.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

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

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

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

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

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

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.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.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

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

Q27.The temperature dependence of resistance of Cu and undoped Si in the temperature range 300 −400 K is best described by JEE Main 2016 (03 Apr) JEE Main Previous Year Paper (1) linear increase for Cu, exponential decrease for (2) linear decrease for Cu, linear decrease for Si Si (3) linear increase for Cu, linear increase for Si (4) linear increase for Cu, exponential increase for Si

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

Q28.Identify the semiconductor devices whose characteristics are given below, in the order (a), (b), (c), (d): (1) Solar cell, Light dependent resistance, Zener (2) Zener diode, Solar cell, Simple diode, Light diode, Simple diode dependent resistance (3) Simple diode, Zener diode, Solar cell, Light (4) Zener diode, Simple diode, Light dependent dependent resistance resistance, Solar cell

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

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

Q29.A realistic graph depicting the variation of the reciprocal of input resistance in an input characteristics measurement in a common emitter transistor configuration is : (1) (2) (3) (4)