physics ONLINE TEST 0% 12th Physics One Mark Test – Full Wish you all the Best ! -St. Joseph Study Centre 1 / 90 The barrier potential of a silicon diode is approximately,? 0.3 V 0.7 V 2.2 V 2.0 V 2 / 90 In a hydrogen atom, the electron revolving in the fourth orbit, has angular momentum equal to? 4h / Π h h / Π 2h / Π 3 / 90 The half-life period of a radioactive element A is same as the mean life time of another radioactive element B. Initially both have the same number of atoms. Then? A will decay at faster rate than B B will decay at faster rate than A A and B have the same decay rate initially A and B decay at the same rate always 4 / 90 Two radiations with photon energies 0.9 eV and 3.3 eV respectively are falling on a metallic surface successively. If the work function of the metal is 0.6 eV, then the ratio of maximum speeds of emitted electrons in the two cases will be ? 1:3 1:9 1:4 1:1 5 / 90 A plane glass is placed over a various coloured letters (violet, green, yellow, red) The letter which appears to be raised more is,? red violet yellow green 6 / 90 In an electron microscope, the electrons are accelerated by a voltage of 14 kV. If the voltage is changed to 224 kV, then the de Broglie wavelength associated with the electrons would? decrease by 4 times increase by 2 times decrease by 2 times increase by 4 times 7 / 90 First diffraction minimum due to a single slit of width 1.0×10⁻⁵ cm is at 30⁰. Then wavelength of light used is,? 700 Å 400 Å 500 Å 600 Å 8 / 90 The speed of light in an isotropic medium depends on? its intensity the nature of propagation the motion of the source w.r.t medium its wavelength 9 / 90 In CE single stage amplifier, the voltage gain at mid – frequency is 10. The voltage gain at upper cut off frequency is? 10 14.14 7.07 20 10 / 90 Which of the following is a secondary cell? Edison cell Leclanche cell Daniel cell Voltaic cell 11 / 90 What is the angle between the electric dipole moment and the electric field strength due to it on the equatorial line? None of these 90° 0° 180° 12 / 90 A photoelectric cell is illuminated by a point source of light 1 m away. When the source is shifted to 2 m then? Number of electrons emitted is a quarter of the initial number Each emitted electron carries half the initial energy Number of electrons emitted is half the initial number Each emitted electron carries one quarter of the initial energy 13 / 90 The explosion of an atom bomb is based on the principle of? fusion reaction thermo nuclear reaction controled fission reaction uncontrolled fission reaction 14 / 90 The dimension of 1 / μ₀ℇ₀ is? [ L ⁻² L²] [ L T ⁻¹] [ L ² T⁻²] [ L⁻¹ T] 15 / 90 The unit of reduction factor of tangent galvanometer is? No unit Tesla Ampere / Degree Ampere 16 / 90 The variation of frequency of carrier wave with respect to the amplitude of the modulating signal is called? Frequency modulation Amplitude modulation Pulse width modulation Phase modulation 17 / 90 An object is placed in front of a convex mirror of focal length of f and the maximum and minimum distance of an object from the mirror such that the image formed is real and magnified? c and ∞ 2f and c f and O None of these 18 / 90 The work function of aa metal is 3.5 eV. If the stopping potential is -1.2 volt then the energy of the incident photon is? 2.3 eV zero 4.7 eV -3.5 eV 19 / 90 A step-down transformer reduces the supply voltage from 220 V to 11 V and increase the current from 6 A to 100 A. Then its efficiency is? 0.12 1.2 0.9 0.83 20 / 90 The torque on a rectangular coil placed in a uniform magnetic field is large when? The number of turns is large The area of the coil is small The number of turns is less The plane of the coil is perpendicular to the field 21 / 90 Which of the following statement is false for the properties of electromagnetic waves? The energy in electromagnetic wave is divided equality between electric and magnetic vectors These waves do not require any material medium for propagation Both electric and magnetic field vectors attain the maxima and minima at the same place and same time Both electric and magnetic field vectors are parallel to each other and perpendicular to the direction of propagation of waves 22 / 90 A piece of copper and another of germanium are cooled from room temperature to 80 K. The resistance of ? copper increases and germanium decreases each of them decreases each of them increases copper decreases and germanium increases 23 / 90 When a metallic surface is illuminated with radiation of wavelength λ , the stopping potential is V. If the same surface is illuminated with radiation of wavelength 2λ , the stopping potential is V / 4. The threshold wavelength for the metallic surface is? 4λ 3λ 5λ 5/2 λ 24 / 90 Two identical point charges of magnitude – q are fixes as shown in the figure below. A third charge + q is placed midway between the two charges at the point P. Suppose this charge + q is displaced a small distance from the point P in the direction indicated by the arrows, in which direction(s) will + q be stable with respect to the displacement? Both directions A₁ and A₂ Not stable B₁ and B₂ 25 / 90 A wire connected to a power supply of 230 V has power dissipation P₁ . Suppose the wire is cut into two equal pieces and connected parallel to the same power supply. In this case power dissipation is P₂. The e ratio P₂ / P₁ is ? 2 4 1 3 26 / 90 If the length of a copper wire has a certain resistance R then on doubling the length its specific resistance? Will become 1/4th Will be doubled Will become 4 times Will remain the same 27 / 90 A ray of light strikes a glass plate at an angle 60⁰. If the reflected and refracted rays are perpendicular to each other, the refractive index of the glass is,? 3 / 2 2 √3 √(3 / 2) 28 / 90 Light transmitted by Nicol prism is,? elliptically polarised partially polarised unpolarised plane polarised 29 / 90 The principle based on which a solar cell operates is? Recombination Carrier flow Diffusion Photovoltaic action 30 / 90 A toaster operating at 240 V has a resistance of 120 Ω. The e power is? 2 W 400 W 480 W 240 W 31 / 90 In a tangent galvanometer, for a constant current, the deflection is 30°. The plane of the coil is rotated through 90°. Now, for the same current, the deflection will be? 60° 0° 30° 90° 32 / 90 The alloys used for muscle wires in Robots are? Gold copper alloys Shape memory alloys Gold silver alloys Two dimensional alloys 33 / 90 The nuclear force is due to the continuous exchange of particles called? mesons leptons photons hypersons 34 / 90 Electromagnetic wave are? Longitudinal May be longitudinal or transverse transverse Neither longitudinal nor transverse 35 / 90 The speed of electromagnetic waves in independent of? Medium in which it travels Wavelength Frequency Intensity 36 / 90 A current loop in a magnetic field? Experiences a torque whether the field is uniform or non – uniform in all orientations Can be in equilibrium in two orientations, one stable while other is unstable Can be in equilibrium in one orientation Can be in equilibrium in two orientations, which are unstable 37 / 90 The materials used in Robotics are? Silver and gold Steel and aluminum Copper and gold Aluminium and silver 38 / 90 The mass of a ⁷₃Li nucleus is 0.042 u less than the sum of the masses of all its nucleons. The average binding energy per nucleon of ⁷₃Li nucleus is nearly? 23 MeV 5.6 MeV 46 MeV 3.9 MeV 39 / 90 A positively charged particle moving due east enters a region of uniform magnetic field directed vertically upwards. The particles will? Continue to move due East Move in a circular orbit with its speed unchanged Move in a circular orbit with its speed increases Gets deflected vertically upwards 40 / 90 A metal foil of negligible thickness is introduced between two plates of a capacitor at the centre. The capacitance of capacitor will be? Same Double Half K times 41 / 90 In a series resonant RLC circuit, the voltage across 100 Ω resistor is 40 V. The resonant frequency ω is 250 rad/s. If the value of C is 4 μF, then the voltage across L is? 1 V 4000 V 600 V 400 V 42 / 90 A photoelectric surface is illuminated successively by monochromatic light of wavelength λ and λ/2 . 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 material is? hc / 3λ hc / λ 2hc / λ hc / 2λ 43 / 90 The threshold wavelength for a metal surface whose photoelectric work function is 3.313 eV is ? 3750 Å 2062.5 Å 6000 Å 4125 Å 44 / 90 Torque on a dipole in a uniform electric field is maximum when angle between p and E is 180° 45° 90° 0° 45 / 90 The particle size of ZnO material is 30 nm. Based on the dimension it is classified as? Nanomaterial Bulk material Soft material Magnetic material 46 / 90 An inductor 20 mH, a capacitor 50 μF and a resistor 40 Ω are connected in series across a source of emf V = 10 sin 340 t. The power loss in AC circuit is? 0.67 W 0.89 W 0.46 W 0.76 W 47 / 90 Which of the following electromagnetic radiations is used for viewing objects through fog? X- rays gamma rays microwave infrared 48 / 90 The period of revolution of a charged particle inside a cyclotron does not depend on? The velocity of the particle The charge of the particle The magnetic induction The mass of the particle 49 / 90 Two identical conduction balls having positive charges q₁ and q₂ are separated by a center to center distance r. If they are made to touch each other and then separated to the same distance, the force between them will be? More than before Zero Same as before Less than before 50 / 90 The coefficient of self induction of a solenoid is independent of? The area of cross section of the coil The current passing through the coil The number of turns of the coil The length of the coil 51 / 90 The spectral series of hydrogen atom in UV region are called? Paschen series Pfund series Balmer series Lyman series 52 / 90 A carbon resistor of (47 ± 4.7 ) k Ω to be marked with rings of different colours for its identification. The colour code sequence will be? Yellow – Violet – Orange – Silver Yellow – Green – Violet – Gold Green – Orange – Violet – Gold Violet – Yellow – Orange – Silver 53 / 90 The electric and magnetic fields of an electromagnetic wave are? in phase and perpendicular to each other in phase and not perpendicular to each other out of phase and perpendicular to each other out of phase and not perpendicular to each other 54 / 90 Nichrome wire is used as the heating element because it has? Low specific resistance High conductivity Low melting point High specific resistance 55 / 90 The total electric flux for the following closed surface which is kept inside water? q/40 ε˳ q/80 ε˳ 80q/ε˳ q/160 ε˳ 56 / 90 Two point white dots are 1 mm apart on a black paper. They are viewed by eye of pupil diameter 3 mm approximately. The maximum distance at which these dots can be resolved by the eye is, [take wavelength of light, λ = 500 nm] 1 m 5 m 3 m 6 m 57 / 90 A ray of light travelling in a transparent medium of refractive index n falls, on a surface separating the medium from air at an angle of incidents of 45º. The ray can undergo total internal reflection for the following n? n = 1.33 n = 1.25 n = 1.4 n = 1.5 58 / 90 Atomic number of H – like atom with ionization potential 122.4 v for n = 1 is? 3 1 4 2 59 / 90 In J.J. Thomson e/m experiment, a beam of electron is replaced by that of muons (particl with same charge as that of electrons but mass 208 times that of electrons). No deflection condition is achieved only if? B is decreased by 208 times B is increased by 208 times B is decreased by 14.4 times B is increased by 14.4 times 60 / 90 A parallel plate air capacitor is charged to a potential difference of V volt. On disconnecting the charging battery distance between the plates of the capacitor is increased using an insulting handle. As a result the potential difference between the plates? Does not change Decreases Increases Becomes zero 61 / 90 A light source of wavelength 520 nm emits 1.04 × 10¹⁵ photons per second while the second source of 460 nm produces 1.38 × 10¹⁵ photons per second. Then the ratio of power of second source to that of first source is? 0.98 1.02 1.5 1.00 62 / 90 A rod of length 10 cm lies along the principal axis of a concave mirror of focal length 10 cm in such a way that its end closer to the pole is 20 cm away from the mirror. The length of the image is? 2.5 cm 15cm 10 cm 5cm 63 / 90 The time taken by the radioactive element to reduce to 1 / e times is? half life half life / 2 mean life twice the mean life 64 / 90 The zener diode is primarily used as? Voltage regulator Rectifier Oscillator Amplifier 65 / 90 Avalanche breakdown is primarily dependent on the phenomenon of? recombination doping collision ionization 66 / 90 The forbidden energy gap for germanium is of the order of? 10 eV 0.7 eV 0.3 eV 1.1 eV 67 / 90 An air bubble in glass slab of refractive index 1.5 (near normal incidence) is 5 cm deep when viewed from one surface and 3 cm deep when viewed from the opposite face. The thickness of the slab is? 10 cm 8 cm 16 cm 12 cm 68 / 90 The following graph shows current versus voltage values of some unknown conductor. What is the resistance of this conductor? 1 ohm 2 ohm 4 ohm 8 ohm 69 / 90 An electric dipole is placed at an alignment angle of 30° with an electric field of 2 x 10⁵ NC¯¹. It experiences torque equal to 8 Nm. The charge on the dipole if the dipole length is 1cm is? 5 mC 7 mC 4 mC 8 mC 70 / 90 In a Young’s double-slit experiment, the slit separation is doubled. To maintain the same fringe spacing on the screen, the screen-to-slit di stance D must be changed to,? D / 2 2D √2 D D / √2 71 / 90 When light is incident on a soap film of thickness 5×10⁻⁵ cm, the wavelength of light reflected maximum in the visible region is 5320 Å. Refractive index of the film will be,? 1.51 1.33 1.22 1.83 72 / 90 Which of the following is false for electromagnetic waves? produced by accelerating charges longitudinal non-mechanical waves transverse 73 / 90 Of the following devices, which has small resistance? Ammeter of range (0-10) A Ammeter of range (0-1) A Moving coil galvanometer Voltmeter 74 / 90 When the number of turns (n) in a galvanometer is doubled current sensitivity? Decreases twice Increases four times Remains constant Increases twice 75 / 90 When the current changes from +2A to −2A in 0.05 s, an emf of 8 V is induced in a coil. The co-efficient of self-induction of the coil is? 0.1 H 0.8 H 0.4 H 0.2 H 76 / 90 The time taken by the radioactive element to reduce to 1 / e times is? twice the mean life half life mean life half life / 2 77 / 90 Electromagnetic induction is not used in? Room heater Transformer Choke coil AC generator 78 / 90 If the potential of a capacitor having capacity 6µF is increased from 10 V to 20 V, then increase in its energy will be? 9×10¯⁴ J 4×10¯¹⁴ J 4×10¯⁴ J 12×10¯⁶ J 79 / 90 When a biconvex lens of glass having refractive index 1.47 is dipped in a liquid, it acts as a plane sheet of glass. This implies that the liquid must have refractive index? greater than that of glass less than one less than that of glass equal to that of glass 80 / 90 A transformer is used to light a 100 W and 110 V lamp from a 220 V mains. If the main current is 0.5 A the efficiency of the transformer is approximately? 30% 50% 90% 10% 81 / 90 Fraunhofer lines are an example of _______ spectrum? band emission line absorption line emission band absorption 82 / 90 If the velocity and wavelength of light in air is Vₐ and λₐ and that in water is Vw and λw, then the refractive index of water is? Vₐ λₐ / Vw λw λw / λₐ Vw / Vₐ Vₐ / Vw 83 / 90 Two coherent monochromatic light beams of intensities I and 4I are superposed. The maximum and minimum possible intensities in the resulting beam are? 5I and 3I 5I and I 9I and 3I 9I and I 84 / 90 A circle of radius r is drawn with charge +q at the centre. A charge q˳ is moved between two point on the circle. Then work done is? Infinite Zero Negative Positive 85 / 90 Which charge configuration produces a uniform electric field? Uniformly charged spherical shell Point charge Infinite Uniform line charge Uniformly charged infinite plane 86 / 90 The colour of light emmitted by a LED depends on? its reverse bias its forward bias type of semiconductor material the amount of forward current 87 / 90 What is the ratio of the charges |q₁/q₂| for the following electric field line pattern? 1/5 5 11/25 25/11 88 / 90 In a transformer, the number of turns in the primary and the secondary are 410 and 1230 respectively. If the current in primary is 6A, then that in the secondary coil is? 1 A 2 A 18 A 12 A 89 / 90 For light incident from air on a slab of refractive index 2, the maximum possible angle of refraction is? 90º 30º 45º 60º 90 / 90 “Ski wax” is an application of nano product in the field of? Sports Automotive industry Textile Medicine Your score is Note: Once you start the test, you are not allowed to go back. Results won’t be generated if you quit the test. Complete the test within the given time. 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