Solved Paper -2015
VIT
Engineering Entrance Exam
Physics
1. Equal charges q each are placed at the vertices of an equilateral triangle of side r. The magnitude of electric field intensity at any vertex is
(a) 
(b) 
(c) 
(d) 
2. Two points masses, m each carrying charges –q, and +q are attached to the ends of a massless rigid non-conducting wire of length ‘L’. When this arrangement is placed in a uniform electric field, then it deflects through an angle i. The minimum time needed by rod to align itself along the field is
(a) 
(b) 
(c) 
(d) 
3. A condenser of capacitance C is fully charged by a 200 V supply. It is then discharged through a small coil of resistance wire embedded in thermally insulated block of specific heat 250 J/kg-K and of mass 100 g. If the temperature of the block rises by 0.4 K, then the value of C is
(a) 300 μF
(b) 200 μF
(c) 400 μF
(d) 500 μF
4. The capacitance of a parallel plate capacitor with air as medium is 3μF. As a dielectric is introduced between the plates, the capacitance becomes 15 μF. The permittivity of the medium in C2N−1m−2 is
(a) 
(b) 
(c) 
(d) 
5. The masses of three copper wires are in the ratio 2 : 3 : 5 and their lengths are in the ratio 5 : 3 : 2. Then, the ratio of their electrical resistances is
(a) 1 : 9 : 15
(b) 2 : 3 : 5
(c) 5 : 3 : 2
(d) 125 : 30 : 8
6. A 30V-90W lamp is operated on a 120 V DC line. A resistor is connected in series with the lamp in order to glow it properly. The value of resistance is
(a) 10 Ω
(b) 30 Ω
(c) 20 Ω
(d) 40 Ω
7. In a potentiometer experiment, the balancing length of a cell is 560 cm. When an external resistance of 10 Ω is connected in parallel to the cell, the balancing length changes by 60 cm. The internal resistance of a cell is
(a) 1.4 Ω
(b) 1.6 Ω
(c) 0.12 Ω
(d) 1.2 Ω
8. Two sources of equal emf are connected to a resistance R. The internal resistance of these source R. The internal resistance of these sources are r1 and r2(r1 > r2). If the potential difference across the source having internal resistance r2 is zero, then
(a) 
(b) 
(c) 
(d) 
9. An electron of mass 9.0 × 10−31 kg under the action of a magnetic field moves in a circle of radius 2 cm at a speed of 3 × 106 m/s. If a proton of mass 1.8 × 1027 kg was to move in a circle of same radius in the same magnetic field, then its speed will become
(a) 
(b) 
(c) 
(d) 
10. A horizontal rod of mass 0.01 kg and length 10 cm is placed on a frictionless plane inclined at an angle 60° with the horizontal and with the length of rod parallel to the edge of the inclined plane. A uniform magnetic field is applied vertically downwards. If the current through the rod is 1.73 A, then the value of magnetic field induction B for which the rod remains stationary on the inclined plane is
(a) 1 T
(b) 3 T
(c) 2.5 T
(d) 4 T
11. A current of 2 A is flowing in the sides of an equilateral triangle of side 9 cm. The magnetic field at the centroid of the triangle is
(a) 
(b) 
(c) 
(d) 
12. The direction of magnetic field dB due to current element dl at a distance r is the direction of
(a) r × dl
(b) dl × r
(c) 
(d) dl
13. A galvanometer with a scale divided into 100 equal divisions has a current sensitivity of 10 divisions per milliampere and a voltage sensitivity of 2 divisions per millivolt. The galvanometer resistance will be
(a) 4 Ω
(b) 5 Ω
(c) 3 Ω
(d) 7 Ω
14. The earth is considered as a short magnet with its centre coinciding with the geometric centre of earth. The angle of dip ϕ related to the magnetic latitude λ as
(a) 
(b) tan λ = 2 tan ϕ
(c) tan λ = 2 tan ϕ
(d) tan ϕ = 2tan λ
15. Which of the following statement related hysteresis loop is incorrect?
(a) The curve of B against H for a ferromagnetic material is called hysteresis loop
(b) The area of B-H curve is a measure of power dissipated per cycle per unit area of the specimen
(c) Coercitivity is a measure of the magnetic field required to destroy the residual magnetism of ferromagnetic material
(d) The retentivity of a specimen is the measure of magnetic field remaining in the specimen when the magnetising field is removed
16. A magnetic needle lying parallel to the magnetic field requires W units of work to turn it through an angle 45°. The torque required to maintain the needle in this position will be
(a) 
(b) 
(c) 
(d) 
17. An induced emf has
(a) a direction same as field direction
(b) a direction opposite to the field direction
(c) no direction of its own
(d) None of the above
18. A coil of area 5 cm2 having 20 turns is placed in a uniform magnetic field of 103 The normal to the plane of coil makes an angle 30° with the magnetic field. The flux through the coil is
(a) 6.67 × 10−4 wb
(b) 3.2 × 10−5 wb
(c) 5.9 × 10−4 wb
(d) 8.65 × 10−4 wb
19. The current graph for resonance in LC circuit is
(a) 
(b) 
(c) 
(d) 
20. The value of inductance L for which the current is maximum in series LCR circuit with C = 10 μF and ω = 1000 rad/s
(a) 10 mH
(b) 50 mH
(c) 200 mH
(d) 100 mH
21. A ray of light is incident on a plane mirror at an angle of 30°. At what angle with the horizontal must a p lane mirror be placed so that the reflected ray becomes vertically upwards?
(a) 40°
(b) 20°
(c) 30°
(d) 60°
22. A compound microscope having magnifying power 35 with its eye-piece of focal length 10 cm. Assume that the final images is at least distance of distinct vision then the magnification produced by the objective is
(a) −4
(b) 5
(c) 10
(d) −10
23. The refractive index for a prism is given as 
Then, angle of minimum deviation in terms of angle of prism is
(a) 90° − A
(b) 2A
(c) 180° − A
(d) 180° − 2A
24. Two convex lenses of power 2D and 5D are separated by a distance 
The power of optical system formed is
(a) +2 D
(b) −2 D
(c) −3 D
(d) +3 D
25. Two light rays having the same wavelength in vacuum are in phase initially. Then, the first ray ravels a path L1 through a medium of refractive index μ1 while the second ray travels a path L2 through a medium of refractive index μ2. The two waves are then combined to observe interference. The phase difference between the two waves is
(a) 
(b) 
(c) 
(d) 
26. Two polaroids are kept crossed to each other. If one of them is rotated an angle 60°, the percentage of incident light now transmitted through the system is
(a) 10%
(b) 20%
(c) 25%
(d) 12.5%
27. An electromagnetic wave propagating along north lies its electric field vertically upward. The magnetic field vector points towards
(a) downward
(b) east
(c) north
(d) south
28. Pick out the wrong statement.
(a) Gauss’s law of magnetism is given by ∮B ∙ ds = 0
(b) An EM wave is a wave radiated by charge at rest and propagates through electric field only
(c) A time varying electric field is a source of changing magnetic field
(d) Faraday’s law of EM induction is 
29. When sunlight is scattered by atmospheric atoms and molecules the amount of scattering of light of wavelength 880nm is A. Then, the amount of scattering of light of wavelength 330 nm is approximately
(a) 10 A
(b) 20 A
(c) 40 A
(d) 50.5 A
30. The ratio of volume occupied by an atom to the volume of the nucleus is
(a) 105 : 1
(b) 1020 : 1
(c) 1015 : 1
(d) 1 : 1015
31. When a hydrogen atom is raised from ground energy level to excited energy level, then
(a) potential energy increases and kinetic energy decreases
(b) kinetic energy increases and potential energy decreases
(c) Both KE and PE increase
(d) Both KE and PE decrease
32. The half life for α-decay of uranium 92U228 is 4.47 × 108 If a rock contains 60% of original 92U228 atoms, then its age is
[take log 6 = 0.778, log 2 = 0.3]
(a) 1.2 × 107 yr
(b) 3.3 × 108 yr
(c) 4.2 × 109 yr
(d) 6.5 × 109 yr
33. A nuclear transformation is given by Y (n, α) → 3Li7. The nucleus of element Y is
(a) 5Be11
(b) 5B10
(c) 5B9
(d) 6C12
34. The angular momentum of an electron in Bohr’s hydrogen atom whose energy is −3.4 eV, is
(a) 
(b) 
(c) 
(d) 
35. When the momentum of a photon is changed by an amount p′ then the corresponding change in the de-Broglie wavelength is found to be 0.20%. Then, the original momentum of the photon was
(a) 300 p′
(b) 500 p′
(c) 400 p′
(d) 100 p′
36. Suppose a beam of electrons with each electron having energy E0 incident on a metal surface kept in an evacuated chamber. Then,
(a) electrons can be emitted with any energy with maximum of E0
(b) no electrons will be emitted as only photons can emit electrons
(c) electrons can be emitted but all with an energy E0
(d) electrons can be emitted with any energy with a maximum of where ϕ being work function E0 − Φ
37. An n-type semiconductor is
(a) neutral
(b) positively charged
(c) negatively charged
(d) negatively or positively charged depending on the amount of impurity added
38. In the half wave rectifier circuit operating with 50 Hz mains frequency. The fundamental frequency in the ripple will be
(a) 100 Hz
(b) 200 Hz
(c) 50 Hz
(d) 25 Hz
39. The input resistance of a common emitter amplifier is 330 Ω and the load resistance is 5 kΩ A change of base current is 15 μA results in the change of collector current by 1 mA. The voltage gain of amplifier is
(a) 1000
(b) 10001
(c) 1010
(d) 1100
40. To get an output y = 0 from the circuit shown in the figure, the input C must be
(a) 0
(b) 1
(c) either 0 or 1
(d) None of these
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