Practice Questions

Q10.A Carnot freezer takes heat from water at 0oC inside it and rejects it to the room at a temperature of 27oC. The latent heat of ice is 336 × 103 Jkg−1. If 5kg of water at 0oC is converted into ice at 0oC by the freezer, then the energy consumed by the freezer is close to : (1) 1 .51 ×105 J (2) 1 .68 ×106 J (3) 1 .71 ×107 J (4) 1 .67 ×105 J

Q12.In an engine the piston undergoes vertical simple harmonic motion with amplitude 7cm. A washer rests on top of the piston and moves with it. The motor speed is slowly increased. The frequency of the piston at which the washer no longer stays in contact with the piston, is close to : (1) 0.7 Hz (2) 1.9 Hz (3) 1.2 Hz (4) 0.1 Hz

Q13.A toy-car, blowing its horn, is moving with a steady speed of 5 m s−1 , away from a wall. An observer, towards whom the toy car is moving, is able to hear 5 beats per second. If the velocity of sound in air is 340 m s−1 the frequency of the horn of the toy car is close to (1) 680 Hz (2) 510 Hz (3) 340 Hz (4) 170 Hz

Q15.Figure shows a network of capacitors where the number indicates capacitances in micro Farad. The value of capacitance C if the equivalent capacitance between point A and B is to be 1 μF is : (1) 32 μF (2) 31 μF 23 23 (3) 33 μF (4) 34 μF 23 23

Q30.A screw gauge with a pitch of 0.5 mm and a circular scale with 50 divisions is used to measure the thickness of a thin sheet of aluminium. Before starting the measurement, it is found that when the two jaws of the screw gauge are brought in contact, the 45th division coincides with the main scale line and that the zero of the main scale is barely visible. What is the thickness of the sheet if the main scale reading is 0 .5 mm and the 25th division coincides with the main scale line? (1) 0.70 mm (2) 0.50 mm (3) 0.75 mm (4) 0.80 mm JEE Main 2016 (03 Apr) JEE Main Previous Year Paper

Q29.Let Nβ be the number of β particle emitted by 1 gram of Na24 radioactive nuclei having a half life of 15 h. In 7. 5 h, the number Nβ is close to [NA = 6 .023 ×1023 mole−1] (1) 1.75 × 1022 (2) 6.2 × 1021 (3) 7.5 × 1021 (4) 1.25 × 1022

Q16.The magnitude of the average electric field normally present in the atmosphere just above the surface of the Earth is about 150 N/C , directed inward towards the center of the Earth. This gives the total net surface charge carried by the Earth to be : [Given : ∈O= 8.85 × 10−12 C2/N-m2, RE = 6.37 × 106m] (1) −680 kC (2) + 670 kC (3) + 680 kC (4) − 670 kC

Q18.A d.c. main supply of e.m.f. 220 V is connected across a storage battery of e.m.f. 200 V through a resistance of 1 Ω. The battery terminals are connected to external resistance R. The minimum value of R, so that a current passes through the battery to charge it is: (1) 9 Ω (2) 7 Ω (3) 11 Ω (4) 0

Q20.The magnetic field of earth at the equator is approximately 4 × 10−5T. The radius of earth is 6.4 × 106m. Then the dipole moment of the earth will be nearly of the order of : (1) 1020 A m2 (2) 1016 A m2 (3) 1010 A m2 (4) 1023 A m2

Q21.When the rms voltages VL, VC and VR are measured respectively across the inductor L, the capacitor C and the resistor R in a series LCR circuit connected to an AC source, it is found that the ratio VL : VC : VR = 1 : 2 : 3. If the rms voltage of the AC source is 100 V, then VR is close to : (1) 50 V (2) 70 V (3) 100 V (4) 90 V

Q23.A diver looking up through the water sees the outside world contained in a circular horizon. The refractive index of water is 4 , and the diver's eyes are 15 cm below the surface of the water. Then the radius of the circle 3 is : (1) 15×√7 3 cm (2) 15×3√7 cm (3) 15 × 3√7 cm (4) 15 × 3 × √5 cm

Q24.The focal lengths of objective lens and eye lens of a Galilean Telescope are respectively 30 cm and 3.0 cm. Telescope produces virtual, erect image of an object situated far away from it at least distance of distinct vision from the eye lens. In this condition the Magnifying Power of the Galilean Telescope should be : (1) +8. 8 (2) −11. 2 (3) +11. 2 (4) −8. 8 JEE Main 2014 (09 Apr Online) JEE Main Previous Year Paper

Q27.If the binding energy of the electron in a hydrogen atom is 13. 6 eV , the energy required to remove the electron from the first excited state of Li++ is : (1) 13. 6 eV (2) 3. 4 eV (3) 122. 4 eV (4) 30. 6 eV

Q30.A transmitting antenna at the top of a tower has a height 32 m and the height of the receiving antenna is 50 m. What is the maximum distance between them for satisfactory communication in line of sight (LOS) mode? (1) 45. 5 km (2) 54. 5 km (3) 55. 4 km (4) 455 km

Q16.A liquid drop having 6 excess electrons is kept stationary under a uniform electric field of 25.5 kVm−1 . The density of liquid is 1.26 × 103 kg m−3 . The radius of the drop is (neglect buoyancy). (1) 4.3 × 10−7 m (2) 7.8 × 10−7 m (3) 0.078 × 10−7 m (4) 3.4 × 10−7 m

Q17.The earth's magnetic field lines resemble that of a dipole at the centre of the earth. If the magnetic moment of this dipole is close to 8 × 1022Am2 , the value of earth's magnetic field near the equator is close to (radius of the earth = 6.4 × 106 m) (1) 0.6 Gauss (2) 1.2 Gauss (3) 1.8 Gauss (4) 0.32 Gauss

Q21.A series LR circuit is connected to an ac source of frequency ω and the inductive reactance is equal to 2R. A capacitance of capacitive reactance equal to R is added in series with L and R. The ratio of the new power factor to the old one is : JEE Main 2013 (25 Apr Online) JEE Main Previous Year Paper (1) (2) 3 5 √2 √2 (3) (4) 2 2 √3 √5

Q22.A printed page is pressed by a glass of water. The refractive index of the glass and water is 1.5 and 1.33 , respectively. If the thickness of the bottom of glass is 1 cm and depth of water is 5 cm, how much the page will appear to be shifted if viewed from the top ? (1) 1.033 cm (2) 3.581 cm (3) 1.3533 cm (4) 1.90 cm

Q23.A thin glass plate of thickness is 2500 λ ( λ is wavelength of light used) and refractive index μ = 1.5 is inserted 3 between one of the slits and the screen in Young's double slit experiment. At a point on the screen equidistant from the slits, the ratio of the intensities before and after the introduction of the glass plate is : (1) 2 : 1 (2) 1 : 4 (3) 4 : 1 (4) 4 : 3

Q24.The source that illuminates the double − slit in 'double - slit interference experiment' emits two distinct monochromatic waves of wavelength 500 nm and 600 nm , each of them producing its own pattern on the screen. At the central point of the pattern when path difference is zero, maxima of both the patterns coincide and the resulting interference pattern is most distinct at the region of zero path difference. But as one moves out of this central region, the two fringe systems are gradually out of step such that maximum due to on wavelength coincides with the minimum due to the other and the combined fringe system becomes completely indistinct. This may happen when path difference in nm is: (1) 2000 (2) 3000 (3) 1000 (4) 1500

Q27.A copper ball of radius 1 cm and work function 4.47 eV is irradiated with ultraviolet radiation of wavelength 2500 Å . The effect of irradiation results in the emission of electrons from the ball. Further the ball will acquire charge and due to this there will be a finite value of the potential on the ball. The charge acquired by the ball is : (1) 5.5 × 10−13 C (2) 7.5 × 10−13 C (3) 4.5 × 10−12 C (4) 2.5 × 10−11 C

Q28.A 12.5eV electron beam is used to bombard gaseous hydrogen at room temperature. It will emit: (1) 2 lines in the Lyman series and 1 line in the (2) 3 lines in the Lyman series Balmar series (3) 1 line in the Lyman series and 2 lines in the (4) 3 lines in the Balmer series Balmar series

Q29.A diode detector is used to detect an amplitude modulated wave of 60% modulation by using a condenser of capacity 250 pico farad in parallel with a load resistance of 100 kilo ohm. Find the maximum modulated frequency which could be detected by it. (1) 5.31 MHz (2) 5.31 kHz (3) 10.62 MHz (4) 10.62 kHz

Q22.An object 2.4 m in front of a lens forms a sharp image on a film 12 cm behind the lens. A glass plate 1 cm thick, of refractive index 1.50 is interposed between lens and film with its plane faces parallel to film. At what distance (from lens) should object be shifted to be in sharp focus on film? (1) 7.2 m (2) 2.4 m (3) 3.2 m (4) 5.6 m

Q23.We wish to make a microscope with the help of two positive lenses both with a focal length of 20 mm each and the object is positioned 25 mm from the objective lens. How far apart the lenses should be so that the final image is formed at infinity? JEE Main 2012 (12 May Online) JEE Main Previous Year Paper (1) 20 mm (2) 100 mm (3) 120 mm (4) 80 mm