VIT - Unsolved - Physics - 2008

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Vit – Past papers PHYSICS - UNSOLVED PAPER - 2008

SECTION – I: 

SECTION – I Single Correct Answer Type There are five parts in this question. Four choices are given for each part and one of them is correct. Indicate you choice of the correct answer for each part in your answer-book by writing the letter (a), (b), (c) or (d) whichever is appropriate

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01 Two beams of light will not give rise to an interference pattern, if they are coherent they have the same wavelength they are linearly polarized perpendicular to each other they are not monochromatic Problem

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02 A slit of width a is illuminated with a monochromatic light of wavelength . from a distant source and the diffraction pattern is observed on a screen placed at a distance D from the slit. To increase the width of the central maximum one should decrease D decrease a The width cannot be changed Problem

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Problem 03 A thin film of soap solution (n = 1.4) lies on the top of a glass plate (n =1.5).When visible light is incident almost normal to the plate, two adjacent reflection maxima are observed at two wavelengths 400 and 630 nm. The minimum thickness of the soap solution is 420 nm 450 nm 630 nm 1260 nm

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Problem 04 If the speed of a wave doubles as it passes from shallow water into deeper water, its wavelength will be unchanged Halved doubled quadrupled

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Problem 05 A light whose frequency is equal to is incident on a metal whose work function is 2eV. .The maximum energy of the electrons emitted will be 2.49 eV 4.49 eV 0.49 eV 5.49 eV

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Problem 06 An electron microscope is used to probe the atomic arrangements to a resolution of . What should be the electric potential to which the electrons need to be accelerated? 2.5 V 5V 2.5 kV 5 kV

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Problem 07 Which phenomenon best supports the theory that matter has a wave nature? Electron momentum Electron diffraction Photon momentum Photon diffraction

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Problem 08 The radioactivity of a certain material drops to of the initial value in 2 h. The half-life of this radio nuclide is 10 min 20 min 30 min 40 min

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Problem 09 An observer A sees an asteroid with a radioactive element moving by at a speed = 0.3 c and measures the radioactivity decay time to be . Another observer B is moving with the asteroid and measures its decay time as . Then are related as Either (A) or (C) depending on whether the asteroid is approaching or moving away from A

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Problem 10 has 92 protons and 234 nucleons total in its nucleus. It decays by emitting an alpha particle. After the decay it becomes. a. b. c. d.

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Problem 11 X-rays are emitted when there is a transition of electron between the levels n = 2 to n = 1 and n = 3 to n = 1 respectively n = 2 to n = 1 and n = 3 to n = 2 respectively n = 3 to n = 2 and n = 4 to n = 2 respectively n = 3 to n = 2 and n = 4 to n = 3 respectively

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Problem 12 A certain radioactive material starts emitting particles successively such that the end product is . The number of particles emitted are 4 and 3 respectively 2 and 1 respectively 3 and 4 respectively 3 and 8 respectively

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Problem 13 In the circuit shown above, an input of 1 V is fed into the inverting input of an ideal Op-amp A. The output signal will be + 10 V - 10 V 0 V infinity

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Problem 14 When a solid with a band gap has a donor level just below its empty energy band, the solid is an insulator a conductor p-type semiconductor n-type semiconductor

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Problem 15 A p-n junction has acceptor impurity concentration of in the P side and donor impurity concentration of in the N side. What is the contact -potential at the junction? ( kT = thermal energy, intrinsic carrier concentration ) a. b. c. d.

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Problem 16 A Zener diode has a contact potential of 1 V in the absence of biasing. It undergoes Zener breakdown for an electric field of at the depletion region of p-n junction. If the width of the depletion region is , what should be the reverse biased potential for the Zener breakdown to occur? 3.5V 2.5 V 1.5 V 0.5 V

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Problem 17 In Colpitt oscillator the feedback network consists of two inductors and a capacitor two capacitors and an inductor three pairs of RC circuit three pairs of RL circuit

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Problem 18 The reverse saturation of p-n diode depends on doping concentrations depends on diffusion lengths of carriers depends on the doping concentrations and diffusion lengths depends on the doping concentrations, diffusion length and device temperature

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Problem 19 A radio station has two channels. One is AM at 1020 kHz and the other PM at 89.5 MHz. For good results you will use longer antenna for the AM channel and shorter for the FM shorter antenna for the AM channel and longer for the FM Same length antenna will work for both Information given is not enough to say which one to use for which

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Problem 20 The communication using optical fibres is based on the principle of total imemal reflection Brewster angle polarization resonance

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Problem 21 In nature, the electric charge of any system is always equal to half integral multiple of the least amount of charge zero square of the least amount of charge integral multiple of the least amount of charge

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Problem 22 The energy stored in the capacitor as shown in Fig. (a) is . If the battery is replaced by another capacitor of 900 pF as shown in Fig. (b), then the total energy of system is zero

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Problem 23 Equal amounts of a metal are· converted into cylindrical wires of different lengths Land cross-sectional area A. The wire with the maximum resistance-is the one, which has length = L and area = A length = 2 and area = 2A All have the same resistance, as the amount of the metal is the same

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Problem 24 If the .force exerted by an electric dipole on a charge q at a distance of 1 m is F, the force at a point 2 m away in the same direction will be a. b. c. d.

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Problem 25 A solid sphere of radius and volume charge density is enclosed by a hollow sphere of radius with negative surface charge density , such that the total charge in the system is zero, is positive constant and r is the distance from the centre of the sphere. The ratio is: a. b. c. d.

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Problem 26 A solid spherical conductor of radius R has a spherical cavity of radius a (a < R) at its centre. A charge + Q is kept at the centre. The charge at the inner surface, outer surface and at a position r(a < r < R) are respectively + Q, - Q, 0 - Q, + Q, 0 0,-Q, 0 +Q,0, 0

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Problem 27 A cylindrical capacitor has charge Q and length L. If- both the charge and length of the capacitors are doubled, by keeping other parameters fixed; the energy stored in the capacitor remains same Increases two times Decreases two times Increases four times

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Problem 28 Three resistances of each are connected as shown in figure. If the point D, divides the resistance into two equal halves, the resistance between point A and D will be a. b. c. d.

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Problem 29 The resistance of a metal increases with increasing temperature because the collisions of the conducting electrons with the electrons increase the collisions of the conducting electrons with the lattice consisting of the ions of the metal increase the number of mnduction electrons decrease the n,umber of conduction electrons increase

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Problem 30 In the absence of applied potential, the electric current flowing through a metallic wire is zero because the electrons remain stationary the electrons move in random direction with a speed of the order close to that of velocity of light electrons and ions move in opposite direction

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Problem 31 A meter bridge is used to determine the resistance of an unknwon wire by measuring the balance point length l. If the wire is replaced by another wire of same material but with double the length and half the thickness,the balancing point is expected to be a. b. c. 8l d. 16l

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Problem 32 Identify the incorrect statement regarding a superconducting wire transport current flows through its surface transport current flows through the entire area of cross-section of the wire it exhibits zero electrical resistivity and expels applied magnetic field it is used to produce large magnetic field

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Problem 33 A sample of HCl gas is placed in an electric field, of . The dipole moment of each HCl molecule is . The maximum torque that can act on a molecule is a. b. c. d.

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Problem 34 When a metallic plate swings between the poles of a magnet no effect on the plate eddy currents are set tip inside the plate and the direction of the current is along the motion of the plate eddy currents are set up inside the plate and the direction of the current oppose the motion of the plate eddy currents are set up inside the plate

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Problem 35 When an electrical appliance is switched on, it responds almost immediately, because the electrons in the connecting wires move with the speed of light the electrical signal is carried by electromagnetic waves moving with the speed of light the electrons move with the speed which is close to but less than speed of light the electrons are stagnant

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Problem 36 Two identical incandescent light bulbs are connected as shown in the figure. When the circuit is an AC. voltage source of frequency f, which of the following observations will be correct? Both bulbs will glow alternatively Both bulbs will glow with same brightness provided frequency Bulb will light up initially and goes off, bulb will be ON constantly Bulb will blink and bulb will be ON constantly

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Problem 37 A transformer rated at 10 kW is used to connect a 5 kV transmission line to a 240 V circuit. The ratio of turns in the windings of the transformer is 5 20.8 104 40

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Problem 38 Three solenoid coils of same dimension,same number of turns and same number of layers of winding are taken. Coil 1 with inductance was wound using a Mn wire of resistance ; Coil 2 with inductance was wound using the similar wire but the direction of winding was reversed in each layer; Coil 3 with inductance was wound using a superconducting wire. The self-inductance of the coils are a. b. c. d.

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Problem 39 Light travels with a speed of in crown glass of refractive index 1.5. What is the speed of light in dense flint glass of refractive index 1.8? a. b. c. d.

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Problem 40 A parallel beam of fast moving electrons is incident normally on a narrow slit. A screen is placed at a large distance from the slit. If the speed of the electrons is increased, which of the following statement is correct? Diffraction pattern is not observed on the screen in the case of electrons The angular width of the central maximum of the diffraction pattern will increase The angular width of the central maximum will decrease The angular width of the central maximum will remains the same

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