This practice paper consist of 45 objective type questions is based on WBJEE syllabus.
Ques: 3.8 days is the half-life period of a sample. After how many days, the sample will become 1/8th of the original substance
(a) 11.4
(b) 3.8
(c) 3
(d) None of these
Ans. (a)
Ques: At large distance from an electric dipole, the electric field strength varies with the distance r as
(a) 1/r6
(b) 1/r2
(c) 1/r3
(d) 1/r4
Ans. (c)
Ques: A uniform thick rope of length 5 m is resting on a horizontal smooth surface. It is pulled by a force 5N from one end. The tension in the string at 1 m from the force applied is
(a) zero
(b) 1N
(c) 5N
(d) 4N
Ans. (d)
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Ques: Surface area of a soap bubble is 1.3 x 10–4 m2. The work done to double the surface area will be (Surface tension for soap solution, T = 3 x 10–3 N/m)
(a) 23 J
(b) 7.8 x 10–7 J
(c) 2.6 x 10–4 J
(d) 3.9 x 10–7 J
Ans. (b)
Ques: Two bodies are dropped from the windows of running trains on parallel tracks simultaneously. One of the trains is moving at constant velocity and the other is accelerating with initial velocity equal to that of former. Then (neglect air resistance)
(a) the body from uniformly moving train reaches ground first.
(b) both bodies reach ground simultaneously
(c) no conclusion can be drawn from the given data
(d) the body from accelerating train reaches ground first
Ans. (c)
Ques: An X-ray tube is operating at 150 kV and 10 mA. If only 1 % of the electric power is converted into X-rays, the rate at which the target is heated in calories per second is
(a) 3.55
(b) 35.5
(c) 355
(d) 3550
Ans. (c)
Ques: Let v1 be the frequency of series limit of Lyman series, v2 the frequency of the first line of Lyman series and v3 the frequency of series limit of Balmer series. Then which of the following is correct?
(a) v1 –v2 = v3
(b) v2 –v1 = v3
(c) v3 = ½ (v1 + v2)
(d) v1 – v2 = v3
Ans. (a)
Ques: A car starts from rest. It has to cover a distance of 500 m. The coefficient of friction between the road and tyre is 1/2. The minimum time in which the car can cover this distance is (g = 10 m/s2)
(a) 10 sec
(b) 15 sec
(c) 20 sec
(d) 30 sec
Ans. (b)
Ques: A sonic source of frequncy n0 = 272 Hz is moving along a horizontal circle with a constant speed u = 10 m/s a stationary receiver lies in the same plane out side the circle. If speed of the sound in air is 330 m/s then minimum (nmin) and maximum (nmax) frequncies received by the observer will be
(a) nmin = 264 Hz, nmax = 280.5 Hz
(b) nmin = 250 Hz, nmax = 280.5 Hz
(c) nmin = 280 Hz, nmax = 320.5 Hz
(d) nmin = 250 Hz, nmax = 320 Hz
Ans. (a)
Ques: A source is approaching a stationary observer with velocity (1/10)th that of sound. Ratio of observed and real frequencies will be
(a) 9/10
(b) 11/10
(c) 10/11
(d) 10/9
Ans. (d)
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Ques: A cylindrical tube open at both ends has a fundamental frequency f in air. The tube is dipped vertically in water so that half of its length is in water. The fundamental frequency of the air column is now
(a) f/2
(b) 3f/4
(c) f
(d) 2f
Ans. (c)
Ques: A metallic surface ejects n electrons per second when exposed to green colour light of certain intensity I. The long wavelength limit for the surface being 560 nm. If the surface is exposed to same intensity I of green, yellow and red light simultaneously. Then the number of electrons emitted will be
(a) n
(b) 2n
(c) 3n
(d) 9n
Ans. (a)
Ques: In a very good vacuum system in the laboratory , the vacuum attained was 10-13 atm . If the temperature of the system was 300 K , the number of molecules present in a volume of 1 cc is
(a) 2.4 x 106
(b) 4.2 x 104
(c) 1.2 x 104
(d) 0.4 x 104
Ans. (a)
Ques: A body of uniform cross-sectional area floats in a liquid of density thrice its value. The portion of exposed height will be
(a) 2/3
(b) 5/6
(c) 1/6
(d) 1/3
Ans. (a)
Ques: Compressed air in the tube of a wheel of a cycle at normal temperature suddenly starts coming out from the puncture, the air inside:
(a) starts becoming hotter
(b) starts becoming cooler
(c) remains at the same temperature
(d) May become hotter or cooler depending upon the amount of water vapours present
Ans. (b)
Ques: A body is projected up with a velocity equal to 3/4th of the escape velocity from the surface of the earth. The height it reaches is (Radius of the earth = R)
(a) 10R/9
(b) 9R/7
(c) 9R/8
(d) 10R/3
Ans. (b)
Ques: In a coil when current changes from 10 A to 2 A in time 0.1 sec, induced e.m.f. is 3.20 volt. The self-inductance of coil is
(a) 4 H
(b) 0.4 H
(c) 0.04 H
(d) 5 H
Ans. (c)
Ques: A heater coil is cut into two equal parts and only one part is now used in the heater. The heat generated will now be (Assuming potential difference is same in both cases)
(a) one fourth
(b) halved
(c) doubled
(d) four times
Ans. (c)
Ques: Force between two co-axial identical bar magnets whose centres are r metre apart is 4.8 N. If separation is increased to 2r, the force between them is reduced to
(a) 2.4 N
(b) 0.6 N
(c) 1.2 N
(d) 0.3 N
Ans. (d)
Ques: The induction coil works on the principle of;
(a) self-induction
(b) mutual induction
(c) Ampere’s rule
(d) Fleming’s right hand rule
Ans. (b)
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Ques: A bar magnet has a magnetic moment of 2.5 JT–1 and is placed in a magnetic field of 0.2 T. Work done in turning the magnet from parallel to antiparallel position relative to field direction is
(a) 0.5 J
(b) 1 J
(c) 2 J
(d) 0 J
Ans. (b)
Ques: In a second pendulum, mass of bob is 30g . If it is replaced by 90g mass, then its time period will be
(a) 1 s
(b) 2 s
(c) 4 s
(d) 3 s
Ans. (b)
Ques: Suppose energy liberated in the recombination of a hole electron pair is converted to EM radiation. If the maximum wavelength emitted is 660 nm, what is band gap?
(a) 2.875 eV
(b) 3.875 eV
(c) 4.875 eV
(d) 1.875 eV
Ans. (d)
Ques: The ratio of velocity of sound in hydrogen and oxygen at STP is :
(a) 16 : 1
(b) 8 : 1
(c) 4 : 1
(d) 2 : 1
Ans. (c)
Ques: Positively charged particles are projected into a magnetic field. If the direction of the magnetic field is along the direction of motion of the charge particles, the particles get :
(a) accelerated
(b) decelerated
(c) deflected
(d) no changed in velocity
Ans. (d)
Ques: The length, breadth and thickness of a block are given by l = 12 cm, b = 6 cm and t = 2.45 cm. The volume of the block according to the idea of significant figure should be
(a) 2 x 102 cm3
(b) 2 x 105 cm3
(c) 1.763 x 102 cm3
(d) None of these
Ans. (b)
Ques: The electron in a hydrogen atom makes a transition form n = n1 to n = n2 state. The time period of the electron in the initial state (n1) is eight times that in the final state(n2). The possible values of rij and n2 are :
(a) n1 = 8, n2 = 1
(b) n1 = 4, n2 = 2
(c) n1 = 2, n2 = 4
(d) n1 = 1, n2 = 8
Ans. (b)
Ques: An electric line of force in the xy plane is given by equation x2 + y2 = 1. A particle with unit positive charge, initially at rest at the point x=1, y = o in the xy plane
(a) not move at all
(b) will move along straight line
(c) will move along the circular line of force
(d) information is insufficient to draw any conclusion
Ans. (c)
Ques: An air filled parallel plate condenser has a capacity of 2pF. The separation of the plates is doubled and the interspace between the plates is filled with wax. If the capacity is increased to 6 pF, the dielectric constant of wax is :
(a) 2
(b) 3
(c) 4
(d) 6
Ans. (d)
Ques: There are two planets. The ratio of radius of the two planets is K but ratio of acceleration due to gravity of both planets is g. What will be the ratio of their escape velocity?
(a) (Kg)½
(b) (Kg)–½
(c) (Kg)2
(d) (Kg)–2
Ans. (a)
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Ques: The wave theory of light, in its original form, was first postulated by:
(a) Isaac Newton
(b) Christian Huygens
(c) Thomas Young
(d) Augustm Jean Fresnel
Ans. (b)
Ques: An electric field of 1500 V/m and a magnetic field of 0.40 Wb/m2 act on a moving electron. The minimum uniform speed along a straight line the electron could have is:
(a) 1.6 x 1015m/s
(b) 6 x 10-6rn/s
(c) 75 x 103m/s
(d) 75 x 102m/s
Ans. (c)
Ques: An inductor of 2H and a resistance of are connected in series with a battery of 5 V. The initial rate of change of current is
(a) 0.5 A/s
(b) 2.0 A/s
(c) 2.5 A/s
(d) 0.25 A/s
Ans. (c)
Ques: The X-rays beam coming from an X-ray tube will be :
(a) monochromatic
(b) having all wavelengths smaller than a certain minimum wavelength
(c) having all wavelengths larger than a certain minimum wavelength
(d) having all wavelengths lying between a minimum and a maximum wavelength
Ans. (b)
Ques: The optical path of a monochromatic light is the same if it goes through 2 cm of glass or 2.25 cm of water. If the refractive index of water is 1.33, what is the refractive index of glass?
(a) 2.5
(b) 1.75
(c) 1.5
(d) 1.6
Ans. (c)
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Ques: Two transparent media A and B are separated by a plane boundary. The speed of light in medium A is 2.0 ´ 108 m/s and in medium B is 2.5 ´ 108 m/s. The critical angle for which a ray of light from A to B is totally internally reflected is
(a) sin-1(1/2)
(b) sin-1(4/9)
(c) sin-1(4/5)
(d) sin-1(2/3)
Ans. (c)
Ques: An AM transmitter records an antenna current of 10.5 A. The antenna current drops to 10 A when only carrier is transmitted. What is the percentage modulation ?
(a) 55.3%
(b) 65.3%
(c) 45.3%
(d) 75.3%
Ans. (c)
Ques: A convex lens forms an image of an object on a screen. The height of the image is 9 cm. The lens is now displaced untill an image obtained on the screen. The height of this image is 4 cm. The distance between the object and the screen is 90 cm
(a) the height of the object is 12 cm
(b) the height of the object is 8 cm
(c) The height of the object is 6 cm
(d) none of these
Ans. (c)
Ques: A ball whose density is 0.4 x 103 kg/m3 falls into water from a height of 9 cm. To what depth does the ball sink?
(a) 9 cm
(b) 6 cm
(c) 4.5 cm
(d) 2.25 cm
Ans. (b)
Ques: A man of mass 60 kg is holding a vertical pole. The coefficient of static friction between his hands and the pole is 0.5. If he is able to climb up the pole, what is the minimum force F with which he should press the pole with his hand?
(a) 150 N
(b) 300 N
(c) 600 N
(d) 1200 N
Ans. (d)
Ques: The binding energy per nucleon of deuteron (1H2) and helium nucleus (2He4) are 1.1 MeV and 7 MeV respectively. If two deuteron nuclei react to form a single helium nucleus, then energy released is
(a) 13.9 MeV
(b) 26.9 MeV
(c) 23.6 MeV
(d) 19.2 MeV
Ans. (c)
Ques: The average velocity of a particle moving in a straight line, with constant acceleration of 2m/s2 and initial velocity of 5m/s in first five seconds is:
(a) 7.5 m/s
(b) 10 m/s
(c) 15 m/s
(d) 12.5 m/s
Ans. (b)
Ques: Curie temperature is the temperature above which
(a) a paramagnetic material becomes diamagnetic
(b) a ferromagnetic material becomes diamagnetic
(c) a paramagnetic material becomes ferromagnetic
(d) a ferromagnetic material becomes paramagnetic
Ans. (d)
Ques: The displacement of a particle is represented by the following equation s = 3t3 + 7t2 + 5t + 8, where s is in metre and t in second. The acceleration of the particle at t = 1s is
(a) 14 m/s2
(b) 18 m/s2
(c) 32 m/s2
(d) zero
Ans. (c)
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Ques: How many gm of ice at –14°C are needed to cool 200 gm of water from 25°C to 10°C?
(a) 21 gm
(b) 31 gm
(c) 41 gm
(d) 51 gm
Ans. (b)
Ques: A material produces a magnetic field which helps the applied magnetic field; then it is
(a) diamagnetic
(b) paramagnetic
(c) electromagnetic
(d) none of these
Ans. (b)
