physics ONLINE TEST 0% 12th Physics One Mark Test – Full Wish you all the Best ! -St. Joseph Study Centre 1 / 90 Which of the following is false for electromagnetic waves? produced by accelerating charges longitudinal transverse non-mechanical waves 2 / 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 = 1.25 n = 1.4 n = 1.33 n = 1.5 3 / 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 0.9 0.83 1.2 4 / 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? 10% 30% 90% 50% 5 / 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,? 600 Å 500 Å 700 Å 400 Å 6 / 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 ? 3 1 2 4 7 / 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 Number of electrons emitted is half the initial number Each emitted electron carries one quarter of the initial energy Each emitted electron carries half the initial energy 8 / 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? 600 V 400 V 1 V 4000 V 9 / 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? 30° 60° 90° 0° 10 / 90 Avalanche breakdown is primarily dependent on the phenomenon of? ionization doping collision recombination 11 / 90 Light transmitted by Nicol prism is,? unpolarised partially polarised plane polarised elliptically polarised 12 / 90 In a hydrogen atom, the electron revolving in the fourth orbit, has angular momentum equal to? h 4h / Π h / Π 2h / Π 13 / 90 A metal foil of negligible thickness is introduced between two plates of a capacitor at the centre. The capacitance of capacitor will be? Half Double Same K times 14 / 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? 2hc / λ hc / λ hc / 3λ hc / 2λ 15 / 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? f and O 2f and c c and ∞ None of these 16 / 90 The period of revolution of a charged particle inside a cyclotron does not depend on? The charge of the particle The magnetic induction The velocity of the particle The mass of the particle 17 / 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 5cm 10 cm 18 / 90 The following graph shows current versus voltage values of some unknown conductor. What is the resistance of this conductor? 4 ohm 1 ohm 2 ohm 8 ohm 19 / 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? 18 A 1 A 12 A 2 A 20 / 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 Positive Negative 21 / 90 For light incident from air on a slab of refractive index 2, the maximum possible angle of refraction is? 60º 30º 45º 90º 22 / 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? zero 4.7 eV -3.5 eV 2.3 eV 23 / 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 that of glass equal to that of glass less than one 24 / 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? 5.6 MeV 46 MeV 3.9 MeV 23 MeV 25 / 90 Nichrome wire is used as the heating element because it has? High conductivity Low melting point High specific resistance Low specific resistance 26 / 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? Less than before Zero More than before Same as before 27 / 90 The colour of light emmitted by a LED depends on? its forward bias the amount of forward current its reverse bias type of semiconductor material 28 / 90 The barrier potential of a silicon diode is approximately,? 2.2 V 0.7 V 2.0 V 0.3 V 29 / 90 The time taken by the radioactive element to reduce to 1 / e times is? twice the mean life half life / 2 half life mean life 30 / 90 The materials used in Robotics are? Aluminium and silver Copper and gold Silver and gold Steel and aluminum 31 / 90 A plane glass is placed over a various coloured letters (violet, green, yellow, red) The letter which appears to be raised more is,? violet green yellow red 32 / 90 Which charge configuration produces a uniform electric field? Infinite Uniform line charge Uniformly charged spherical shell Uniformly charged infinite plane Point charge 33 / 90 Fraunhofer lines are an example of _______ spectrum? band absorption line emission band emission line absorption 34 / 90 The speed of light in an isotropic medium depends on? the nature of propagation the motion of the source w.r.t medium its intensity its wavelength 35 / 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 D / 2 √2 D 2D 36 / 90 What is the ratio of the charges |q₁/q₂| for the following electric field line pattern? 1/5 5 25/11 11/25 37 / 90 Torque on a dipole in a uniform electric field is maximum when angle between p and E is 180° 0° 45° 90° 38 / 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? 1.5 0.98 1.02 1.00 39 / 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,? 1.33 1.22 1.83 1.51 40 / 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 A and B have the same decay rate initially B will decay at faster rate than A A and B decay at the same rate always 41 / 90 A positively charged particle moving due east enters a region of uniform magnetic field directed vertically upwards. The particles will? Move in a circular orbit with its speed increases Gets deflected vertically upwards Continue to move due East Move in a circular orbit with its speed unchanged 42 / 90 The spectral series of hydrogen atom in UV region are called? Balmer series Lyman series Pfund series Paschen series 43 / 90 “Ski wax” is an application of nano product in the field of? Medicine Automotive industry Textile Sports 44 / 90 If the length of a copper wire has a certain resistance R then on doubling the length its specific resistance? Will be doubled Will become 4 times Will become 1/4th Will remain the same 45 / 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 √(3 / 2) √3 2 46 / 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 47 / 90 The forbidden energy gap for germanium is of the order of? 1.1 eV 10 eV 0.3 eV 0.7 eV 48 / 90 The coefficient of self induction of a solenoid is independent of? The length of the coil The area of cross section of the coil The current passing through the coil The number of turns of the coil 49 / 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? 0.2 H 0.1 H 0.4 H 0.8 H 50 / 90 The explosion of an atom bomb is based on the principle of? controled fission reaction uncontrolled fission reaction thermo nuclear reaction fusion reaction 51 / 90 Electromagnetic wave are? transverse May be longitudinal or transverse Longitudinal Neither longitudinal nor transverse 52 / 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 I 9I and I 9I and 3I 5I and 3I 53 / 90 Which of the following is a secondary cell? Edison cell Leclanche cell Voltaic cell Daniel cell 54 / 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 55 / 90 The alloys used for muscle wires in Robots are? Two dimensional alloys Shape memory alloys Gold copper alloys Gold silver alloys 56 / 90 Atomic number of H – like atom with ionization potential 122.4 v for n = 1 is? 4 2 1 3 57 / 90 The dimension of 1 / μ₀ℇ₀ is? [ L ⁻² L²] [ L ² T⁻²] [ L T ⁻¹] [ L⁻¹ T] 58 / 90 The zener diode is primarily used as? Rectifier Amplifier Oscillator Voltage regulator 59 / 90 The time taken by the radioactive element to reduce to 1 / e times is? mean life half life twice the mean life half life / 2 60 / 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 61 / 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? 4×10¯⁴ J 9×10¯⁴ J 12×10¯⁶ J 4×10¯¹⁴ J 62 / 90 The torque on a rectangular coil placed in a uniform magnetic field is large when? The number of turns is less The plane of the coil is perpendicular to the field The area of the coil is small The number of turns is large 63 / 90 The electric and magnetic fields of an electromagnetic wave are? out of phase and not perpendicular to each other in phase and not perpendicular to each other out of phase and perpendicular to each other in phase and perpendicular to each other 64 / 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? increase by 4 times decrease by 4 times increase by 2 times decrease by 2 times 65 / 90 The unit of reduction factor of tangent galvanometer is? Ampere Tesla No unit Ampere / Degree 66 / 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 0.76 W 0.89 W 0.46 W 67 / 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? 4 mC 5 mC 7 mC 8 mC 68 / 90 The total electric flux for the following closed surface which is kept inside water? q/80 ε˳ q/40 ε˳ q/160 ε˳ 80q/ε˳ 69 / 90 The threshold wavelength for a metal surface whose photoelectric work function is 3.313 eV is ? 2062.5 Å 3750 Å 4125 Å 6000 Å 70 / 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 ? 1:9 1:1 1:4 1:3 71 / 90 The speed of electromagnetic waves in independent of? Medium in which it travels Frequency Wavelength Intensity 72 / 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 14.4 times B is decreased by 208 times B is increased by 208 times B is increased by 14.4 times 73 / 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? 5λ 4λ 3λ 5/2 λ 74 / 90 In CE single stage amplifier, the voltage gain at mid – frequency is 10. The voltage gain at upper cut off frequency is? 10 7.07 20 14.14 75 / 90 Which of the following electromagnetic radiations is used for viewing objects through fog? X- rays infrared microwave gamma rays 76 / 90 Electromagnetic induction is not used in? Room heater AC generator Transformer Choke coil 77 / 90 What is the angle between the electric dipole moment and the electric field strength due to it on the equatorial line? 0° 180° None of these 90° 78 / 90 A toaster operating at 240 V has a resistance of 120 Ω. The e power is? 480 W 240 W 400 W 2 W 79 / 90 A current loop in a magnetic field? Can be in equilibrium in one orientation Can be in equilibrium in two orientations, one stable while other is unstable Can be in equilibrium in two orientations, which are unstable Experiences a torque whether the field is uniform or non – uniform in all orientations 80 / 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] 6 m 1 m 3 m 5 m 81 / 90 A piece of copper and another of germanium are cooled from room temperature to 80 K. The resistance of ? each of them decreases each of them increases copper increases and germanium decreases copper decreases and germanium increases 82 / 90 The particle size of ZnO material is 30 nm. Based on the dimension it is classified as? Nanomaterial Bulk material Magnetic material Soft material 83 / 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 / Vw λw / λₐ Vₐ λₐ / Vw λw Vw / Vₐ 84 / 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 B₁ and B₂ Not stable 85 / 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 are parallel to each other and perpendicular to the direction of propagation of waves Both electric and magnetic field vectors attain the maxima and minima at the same place and same time 86 / 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? Becomes zero Does not change Decreases Increases 87 / 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? 12 cm 8 cm 10 cm 16 cm 88 / 90 When the number of turns (n) in a galvanometer is doubled current sensitivity? Decreases twice Increases twice Increases four times Remains constant 89 / 90 The principle based on which a solar cell operates is? Diffusion Recombination Photovoltaic action Carrier flow 90 / 90 The nuclear force is due to the continuous exchange of particles called? photons mesons leptons hypersons 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. Once the time is over, the test will be submitted automatically. You can verify your answers at the result page.